Temperature Converter

This free temperature converter converts between the units people in the United States actually use every day and the metric units used in science, in most other countries, and in many products sold online. Type a value, choose the unit it is in, choose the unit you want, and the answer appears at once, together with the same value in every other supported unit and the formula that produced it. Nothing is sent to a server, nothing needs a sign in, and the result is ready before you touch a field, because the default value is already converted when the page loads.

What Is a Temperature Converter?

A good temperature converter converts between the units people in the United States actually use every day and the metric units used in science, in most other countries, and in many products sold online. Type a value, choose the unit it is in, choose the unit you want, and the answer appears at once, together with the same value in every other supported unit and the formula that produced it. Nothing is sent to a server, nothing needs a sign in, and the result is ready before you touch a field, because the default value is already converted when the page loads.

A temperature converter measures warmth on scales that differ in two ways at once: the size of one degree, and the point called zero. The warmth itself does not change when the scale changes, but the number does not follow the simple larger unit, smaller number rule that works for length or weight, because each scale starts somewhere different. Fahrenheit calls the freezing point of water 32 degrees, Celsius calls it 0 degrees, and kelvin calls it 273.15, so converting a temperature always needs a shift as well as a scale change. That offset is why a temperature of 68 degrees Fahrenheit is 20 degrees Celsius, even though neither number is a simple multiple of the other, and why converting a temperature difference follows different rules from converting a temperature value.

The units on this page fall into two families. The United States customary units grew out of English practice and remain standard in daily life in the United States for driving, building, shopping, and weather. The metric units are built on powers of ten around a single base unit, which makes them natural for science, for international trade, and for any calculation that chains several steps together. Both families describe the same physical world, and the converter bridges them with factors that are fixed by definition, not by measurement, so the same input always gives the same output. The temperature converter on this page also links well with the BMI calculator when a quantity needs a second step, such as turning a converted length into an area or a converted weight into a daily target.

One habit will make every conversion easier: always name the starting unit and the target unit before you look at the number. A bare number such as 150 means nothing until you know whether it is pounds, kilograms, miles, or something else, and most conversion errors are really unit errors, not arithmetic errors. Say the units out loud, check that the From box matches the unit on your source, check that the To box matches the unit you need, and only then read the result. The all-units panel below the main result helps here, because it shows the same value in every unit at once, and a value that looks wrong in one row will usually look right in a row you already understand, which tells you at once whether the input unit was the problem.

How to Use This Temperature Converter

Using this converter takes less than a minute, and the steps below work the same way for every pair of units. The calculator updates the instant you type or change a selection, so there is no button to press and no page to reload. Start with the default value already on screen, change it to your own number, and watch the result, the formula, and the all-units panel change together. If you change your mind about direction, use the swap control instead of retyping, because swapping keeps your number and exchanges the two units in one move.

1. Enter your value in the first box. You can type whole numbers, decimals, and, for temperature, negative values. Use a plain number with no unit symbol and no commas, so the calculator reads it cleanly.
2. Choose the unit your value is already in from the From list. This is the unit printed on your source: the road sign, the label, the recipe, the thermostat, or the plan.
3. Choose the unit you want from the To list. The large result at the top of the result box is this conversion, and it is the number to copy or to use in your next step.
4. Read the formula line under the result. It shows the factor that was applied, so you can check the work, repeat it by hand, or reuse the factor in a spreadsheet.
5. Check the all-units panel. It shows the same value in every supported unit, which is useful when you need two results at once or when you want to sense check a value against a unit you know well.
6. Change the decimal places if you need more or less detail. Two places suit everyday answers, four places suit checking, and six places suit a number that will feed another calculation.

Using the Swap Control

The swap control exchanges the From and To units and recalculates at once. It is the fastest way to reverse a conversion: convert a value in one direction, swap, and you are converting the same quantity back, which should return the starting number apart from display rounding. Swapping is also the best way to learn a pair of units, because you can watch how the factor flips. A factor larger than one in one direction becomes its reciprocal, smaller than one, in the other direction, and seeing both directions side by side makes the relationship stick. If you swap and the answer does not look like the reverse of the previous answer, check that you did not also change the value box in between.

Reading the All-Units Panel

Below the main result, the panel lists every supported unit with the converted value beside it. Use it when a task needs more than one unit, for example when a shipping form wants kilograms while a recipe wants grams, or when one form wants one unit and another wants a different unit. The panel also protects against a common mistake: choosing the wrong From unit. If the panel shows a value you know is wrong in a familiar unit, the From unit is probably wrong, and fixing it fixes every row at once. Read the panel from the unit you trust most, then move to the unit you need.

Working With Zero, Empty, and Unusual Inputs

An empty box shows a short prompt instead of a made up number, because an empty input has no answer. Zero is a real answer for most quantities on this page: zero in any unit is zero in every other unit, and the converter shows that plainly. Very large and very small values are shown in a compact form when they would otherwise fill the box with digits, and the decimal places control still applies. For temperature, values below absolute zero are refused with an explanation, because no such temperature can exist. For the other converters, a negative value is refused with an explanation, because a negative distance, weight, speed, or area has no everyday meaning.

How Temperature Conversion Works

Every conversion on this page follows the same two-step route, and understanding that route explains why the results are consistent in every direction. First, the starting value is multiplied by the size of its unit measured in the base unit, which turns it into a base unit value. Second, that base unit value is divided by the size of the target unit measured in the same base unit, which turns it into the target unit. The base unit here is Celsius. No step in between is rounded, so converting from a unit to the base and back returns the starting value, and converting through an intermediate unit gives the same answer as converting directly.

Temperature is the one exception to the pure multiply and divide pattern, because its scales do not share a zero point. Fahrenheit and Celsius differ in both the size of a degree and the position of zero, and kelvin shares the Celsius degree size but starts at absolute zero. A temperature conversion therefore needs an offset as well as a scale factor, and the converter handles that by routing through Celsius: Fahrenheit values are shifted and scaled into Celsius, Celsius values are shifted into kelvin, and the reverse steps undo the shift. The formula line shows the exact offset and factor for the pair you chose, so a temperature result can always be checked by hand. The National Institute of Standards and Technology publishes the definitions behind the metric units, and its guidance is the authority for the exact factors used here.

Why One Base Unit Beats a Table of Pairs

A converter could store a separate factor for every pair of units, but that approach grows quickly and invites inconsistency: with nine units there are seventy two directed pairs, and a single typo in one pair would make that pair disagree with every other route. Routing through one base unit needs only one factor per unit, and every pair is then built from the same two numbers. The result is that any round trip returns to its start, any chain of conversions agrees with the direct conversion, and a correction to one factor fixes every pair that uses it. It is the same reason maps use a single scale: one reference keeps every distance on the same footing.

Exact Factors and Rounded Factors

Some factors on this page are exact by definition. An inch is exactly 2.54 centimeters, a foot is exactly 0.3048 meters, a pound is exactly 0.45359237 kilograms, and a mile is exactly 1,609.344 meters, because the international yard and pound agreement of 1959 fixed them. Other factors are exact in a different way: a kilometer is exactly 1,000 meters by the construction of the metric system. Where a factor is a repeating decimal in the display, such as kilometers per hour to meters per second, the converter keeps the full stored value and only rounds what you see. That distinction matters when a result feeds another calculation, because rounding early compounds, while rounding once at the end keeps the error smaller than the last displayed digit.

Conversion Factors for Every Unit

The table below lists every supported unit, its size in the base unit, how the factor is defined, and a memory hook that helps you place it. Read it as a reference, not as something to memorize in full: the two or three units you use most are worth learning by heart, and the rest can be looked up here whenever they appear. Notice how the United States customary units relate to each other in small whole numbers, 12, 3, 1,760, 16, 14, and 2,000, while the metric units relate in powers of ten. That difference explains why mental conversion inside one family feels easy and conversion between families feels hard: inside a family you multiply by a familiar whole number or shift a decimal point, while between families you need a factor that is not a round number.

Keep this table open beside the converter when you work with an unfamiliar unit for the first time. Find your starting unit, find your target unit, and compare their sizes in the base unit: the larger unit will always give the smaller number, and the ratio of the two sizes is the factor the converter applies. If the ratio is close to one, the two units are close in size and the numbers will look similar. If the ratio is far from one, expect a very different looking number for the same quantity, and do not let that surprise you into thinking the conversion is wrong. A quick check against a row you already know, such as 1 mile or 150 pounds, will usually settle the question in seconds.

Common Conversions at a Glance

The common conversions table below covers the pairs people search for most often, with the values already worked out so you can read them without typing. Use it as a quick lookup when you are in a hurry, and use the converter above when your number is not in the table or when you need a different number of decimal places. The values are rounded to four decimal places in the table, while the converter can show two, four, or six, so a small difference in the last digit between the table and the converter is display rounding, not a different answer.

A pattern worth noticing in the table is that the same starting value can look very different in different units without any contradiction. One mile is 1.6093 kilometers, 5,280 feet, and 63,360 inches, and all three statements describe the same road. The habit of reading the unit before the number prevents the most common reading error, which is to compare two numbers from different units as if they were the same kind of thing. When you copy a value from this table into a form, a shopping cart, or a plan, copy the unit with it, or write the unit beside it at once, because a number without its unit will be misread later, often by yourself.

• Check the unit on your source before you look up a row, because the same number in a different unit needs a different row.
• Read across the row, not down the column, when you want all the forms of one starting value.
• Use the converter, not the table, when your starting value is not listed, because interpolating between rows is guesswork.
• Keep the decimal places control in mind: the table rounds to four places, and a value that needs more detail belongs in the converter.
• When two rows disagree with your expectation, trust the factor table and the formula line, and recheck the starting unit first.

Everyday Examples in the United States

Conversions stop being abstract the moment they touch a daily task, and the United States runs on a mix of units that makes conversion a daily skill rather than a school exercise. A driver reads miles, a weather report speaks Fahrenheit, a grocery label lists ounces and grams, a house listing quotes square feet, and a science class asks for meters and kilograms, often in the same week. The examples below put each unit in the setting where Americans meet it first, so the numbers have a home in memory instead of floating as isolated facts. The water intake calculator is a useful next step when a converted value needs to become a share, a change, or a comparison, because it handles the percentage step with the same instant, formula shown approach.

At Home and on the Road

At home, the units are close to the body and the room: height in feet and inches, room sizes in feet, oven settings in Fahrenheit, and package weights in pounds and ounces. On the road, the units stretch out: distances in miles, speed limits in miles per hour, fuel economy in miles per gallon, and trip times in hours. The jump from home scale to road scale is where conversion errors bite, because a distance that feels short in miles can be long in minutes at city speed, and a room that feels large in square feet can be small in square meters. Keeping a few home and road reference values in mind, a doorway, a room, a city block, and a highway hour, gives you a scale to judge every new conversion against.

At Work, at School, and Online

At work and at school, the unit often comes from a standard, a specification, or a textbook, and the converter is the bridge between that standard and the unit you think in. A product page may list centimeters while your tape measure reads inches, a lab sheet may ask for kilograms while your scale reads pounds, and a foreign weather forecast may speak Celsius while your thermostat speaks Fahrenheit. Online shopping makes this constant: the same item can be listed in inches on one site and centimeters on another, and comparing the two listings without converting is comparing unlike with unlike. In each case, convert first, compare second, and keep the unit attached to the number through the whole decision, from the first look to the final order.

• Height, room size, and furniture: feet and inches first, metric as the check.
• Road distance and speed: miles and miles per hour first, kilometers as the check.
• Weather, ovens, and body temperature: Fahrenheit first, Celsius as the check.
• Body weight, groceries, and luggage: pounds and ounces first, kilograms as the check.
• Land, lots, and floor area: square feet and acres first, square meters and hectares as the check.
• Science, lab work, and homework: metric first, United States customary units as the check.

Worked Examples, Step by Step

Worked examples are the fastest way to learn a conversion, because they show the factor, the arithmetic, and the check in one place. The examples below use round numbers where possible, so the arithmetic can be followed without a calculator, and they cover both directions, so you can see how the factor flips. Try each one in the converter above after reading it: type the starting value, set the units, and confirm that the converter agrees. If it does not, the most likely cause is a swapped From and To, and the swap control will fix it in one move.

Worked Example in Full

Take the default value on this page and work it by hand, step by step, so the method is visible. Start with the value in its starting unit, multiply by the size of that unit in the base unit, and divide by the size of the target unit in the same base unit. Write the units beside each number as you go, and cancel the units that appear on both sides of the division, leaving only the target unit. That unit check, sometimes called dimensional analysis, catches most errors before they reach an answer: if the units do not cancel to the target unit, the factor is upside down. Finish by estimating: the result should be larger than the starting value when the target unit is smaller, and smaller when the target unit is larger, and a result that breaks that rule has a flipped factor.

Worked Example in the Other Direction

Now reverse the same example. Start with the result you just found, swap the From and To units, and convert back. The answer should return to the starting value, apart from the last displayed digit, because the forward and reverse factors are reciprocals. If the return journey lands far from the start, one of the two factors is wrong, or the decimal places setting changed the display in a way that looks larger than it is. This round trip test is worth running whenever a conversion will be used for money, for a cut, for a dose, or for a legal record, because it takes seconds and it proves the factor in both directions at once. The basic calculator helps with the same round trip habit for ordinary arithmetic, when a converted value still needs adding, subtracting, or averaging.

Choosing the Right Unit

Choosing the right unit is a judgment about the reader, the tool, and the size of the quantity, not a matter of taste alone. The right unit is the one that gives a number between about one and a few thousand, with no more digits than the job needs, in the unit the reader already understands. A room measured in miles gives a tiny decimal that is hard to picture, and a road trip measured in inches gives a huge number that is hard to use, even though both are technically correct. Match the unit to the scale, match it to the audience, and match it to the tool that will measure or cut or weigh the result.

Reading a Number at the Right Scale

A number is easiest to use when it sits in the range people can picture without counting digits. One to one hundred is ideal for everyday talk, one hundred to ten thousand is fine for a specification, and anything beyond that usually deserves a larger unit. If your result has five digits before the decimal point, step up to a larger unit and watch it shrink to two or three digits. If your result is a small decimal with several leading zeros, step down to a smaller unit and watch it grow into a readable number. The converter makes stepping up and down cheap, because changing the To unit recalculates at once, so try two neighboring units and pick the one that reads most clearly.

Precision, Rounding, and Significant Figures

Precision is how many digits you keep, and it should follow the precision of your input, not the precision of the calculator. A value measured to the nearest inch cannot honestly become a metric value to four decimal places, because the extra digits imply a measurement accuracy you do not have. Keep the full precision through the calculation, round only the final display, and round to the same number of meaningful digits as your least precise input. The decimal places control on this page lets you do that deliberately: choose two places for a spoken answer, four for a written record, and six only when the number will feed another calculation. When in doubt, show one more digit than you think you need and say that the value is rounded, rather than hiding the rounding entirely.

Rounding, Precision, and Checking Your Answer

Rounding is where good conversions quietly go wrong, because rounding early and rounding often both shift the answer. The rule that protects you is simple: never round until the end. Carry the full value through every step, including any intermediate conversion through the base unit, and round only the number you display or record. A factor rounded to two digits, such as 1.6 for miles to kilometers, is fine for an estimate, but a chain of estimates built on rounded factors can drift by several percent, which is enough to miss a cut, overshoot a dose, or misprice a shipment. The converter follows the rule for you: it stores the full factor, calculates at full precision, and rounds only the display.

• Round only the final answer, never an intermediate step.
• Match the displayed digits to the precision of the measurement you started with.
• Use more decimal places when the result will feed another calculation.
• Say that a value is approximate when you have rounded it for display.
• Check a rounded answer by converting back: the return trip should land close to the start.
• When a total is built from many parts, round the total, not each part, or the parts will not add up.

Estimating Before You Calculate

An estimate made before you type is a safety net, not a waste of time. Round the starting value to a friendly number, apply a friendly factor, and hold the rough answer in mind. Then type the exact value and compare: if the exact answer is close to the estimate, you probably chose the right units and the right direction. If the exact answer is far from the estimate, stop and check the From and To boxes before you trust it, because a factor applied upside down or a wrong starting unit both produce answers that are far off in a way that an estimate exposes at once. Estimates also help in conversation, where a rough answer now is often more useful than an exact answer later.

Common Mistakes and How to Avoid Them

Most conversion mistakes are not arithmetic mistakes. They are unit mistakes, direction mistakes, or rounding mistakes, and they share a pattern: the arithmetic is correct, the units are wrong, and the answer looks plausible enough to pass unnoticed. The list below names the mistakes that appear most often with this kind of converter, with a fix for each one. Read it once, and keep it in mind whenever a result surprises you, because a surprising result is usually a signal, not a mystery.

• Choosing the wrong From unit, so a value in one unit is treated as if it were in another. Fix: check the unit on the source before you type.
• Applying the factor upside down, so a large unit gives a large number instead of a small one. Fix: remember that a larger unit means a smaller count.
• Mixing units inside one calculation, such as adding feet to inches without converting first. Fix: convert every term to one unit before you add or subtract.
• Rounding an intermediate step, so the error grows through the rest of the calculation. Fix: round only at the end.
• Using a rounded factor from memory for a job that needs the exact factor. Fix: use the converter factor, and use the memory factor only for estimates.
• Confusing units with similar names, such as a short ton and a metric tonne, or a statute mile and a nautical mile. Fix: check the definition, not just the name.
• Forgetting an offset, especially with temperature, where multiplying alone cannot work because the zero points differ. Fix: use the full formula with its offset.
• Dropping the unit when copying a result, so the number is later read in the wrong unit. Fix: copy the unit with the number, every time.

Mistakes That Change the Answer Quietly

The quietest mistakes are the ones that change the answer by a small amount, because they pass a quick glance. A factor rounded from 1.609344 to 1.6 changes a 100 mile trip by less than a kilometer, which looks harmless, but the same rounding applied to a thousand mile freight plan changes the total by nearly ten kilometers. A temperature converted without its offset can be wrong by 32 degrees, which is obvious, but a temperature difference converted as if it were a temperature can be wrong by a smaller amount that still ruins a recipe or a lab result. The defense against quiet mistakes is the same in every case: show the formula, check the units, estimate first, and convert back. If any of those checks disagrees, trust the check over the first answer and find the step that broke.

Checking Your Answer in Thirty Seconds

A thirty second check catches almost every conversion error. First, read the unit beside the answer and say the sentence out loud: the starting value in its unit equals the answer in its unit. Second, estimate with a friendly factor and confirm the answer is in the same neighborhood. Third, swap the units and convert back, and confirm you return near the start. Fourth, look at the all-units panel and confirm that a familiar unit shows a value you recognize. If all four checks pass, the answer is almost certainly right. If any check fails, the error is in the input unit, the direction, or the factor, and finding it is usually a matter of reading the From and To boxes again with fresh eyes.

History of the Units: Customary and Metric

Measurement units were not handed down complete. They grew from the human body, from farming, from trade, and from the needs of builders and sailors, and each unit carries that history in its size. The foot was a foot, the yard was a pace or an arm span, the acre was the land a team could plow in a day, and the mile was a thousand paces. Those origins explain why the United States customary units relate in uneven numbers: they were standardized after they were already in use, by fixing the sizes people already used, rather than designed from scratch. The metric system took the opposite path: it was designed in France in the 1790s around a single base unit and powers of ten, with the meter defined from the Earth itself, and it spread because that design makes calculation and conversion simple.

The bridge between the two families was built in 1959, when the international yard and pound agreement fixed the inch at exactly 2.54 centimeters and the pound at exactly 0.45359237 kilograms. From that day, every United States customary unit of length and weight could be expressed exactly in metric terms, and every conversion between the families became a matter of arithmetic rather than of remeasuring. The National Oceanic and Atmospheric Administration records those definitions and the work that keeps them consistent, and the factors on this page follow them exactly. Later, the meter itself was redefined in terms of the speed of light, which made the metric system independent of any physical object, while the customary units kept their exact metric definitions, so the bridge stayed firm even as the foundations changed.

The United States Customary System

The United States customary system is the set of units used in daily life in the United States: inches, feet, yards, and miles for length, ounces, pounds, stones in limited use, and short tons for weight, Fahrenheit for temperature, miles per hour for speed, and square feet and acres for area. It is a living system, not a museum piece: road signs, building codes, property deeds, recipes, and weather reports all use it, and changing any one of those would mean changing the records and habits built around it. Its strengths are familiarity and human scale: a foot is easy to picture, a pound is easy to lift in the mind, and a mile is a natural unit for a journey. Its weakness is conversion between families, which needs the exact factors this page provides.

The Metric System and the International System

The metric system, formalized as the International System of Units, builds every unit from a small set of base units and decimal prefixes. Length starts from the meter, mass from the kilogram, temperature from the kelvin, and area from the square meter, and larger and smaller units are made by multiplying or dividing by ten, one hundred, or one thousand. That structure makes conversion inside the metric family a matter of moving a decimal point, and it makes scientific calculation straightforward, because units combine without extra factors. The metric system is standard in science and in most countries, and it is the language of international trade, medicine, and engineering, which is why even Americans who think in customary units meet metric units on labels, in classrooms, and online every day.

Where Each Unit Is Used: Jobs and Everyday Life

Different jobs need different units, and the same quantity can be the center of a whole profession in one unit and a footnote in another. A builder thinks in feet and inches until a European fitting arrives in millimeters. A farmer thinks in acres until a seed supplier quotes hectares. A pilot thinks in knots until a passenger asks for miles per hour. The table below maps the main fields to the units they use first, so you can see at a glance which unit to reach for in each setting, and which unit to convert into when you hand a number to someone in another field.

• Construction: convert the plan once, write the converted sizes on the plan, and work from the converted plan, not from memory.
• Travel: convert speed limits and distances before you drive in a new country, not while you are driving.
• Cooking: convert a whole recipe at once, including the oven setting, so no single ingredient is left in the old unit.
• Health: record weight and temperature in the unit your clinician uses, and keep the other unit as a check.
• Shipping: confirm which ton, which ounce, and which pound a carrier means before you pay, because the names repeat across systems.
• School: show the factor and the unit cancellation in homework, because the working earns the credit even when a digit slips.

The practical lesson across all these fields is the same: convert at the boundary, not in the middle of the work. When a number crosses from one team, one country, or one system to another, convert it at the crossing, label it clearly, and let everyone downstream work in the new unit. Converting in the middle, by different people with different factors, is how a project ends up with two versions of the same size. The converter on this page is built for that boundary moment: one input, one factor, one clear result, and an all-units panel that lets the next person read the same value in their own unit without a second conversion. The percentage calculator is the natural partner when the next step after conversion is a share or a change, and the length converter covers the distance step that often comes before an area or a travel time.

Mental Shortcuts for Quick Estimates

Mental shortcuts will not replace a converter, but they make you faster and safer, because they let you estimate before you type and judge a result after you read it. The shortcuts below use friendly numbers that are close enough to judge with and far enough from the exact factor that you should still type the exact value when the answer matters. Learn one shortcut per pair you use often, practice it on a value you already know, and it will become automatic. The table gives the shortcut, the exact factor beside it in spirit, and a worked friendly example, so you can see how close the shortcut lands.

1. Pick one shortcut per pair you use weekly, and ignore the rest until you need them.
2. Practice the shortcut on a value you know well, such as your own height or a familiar trip, so the shortcut has a reference point.
3. Use the shortcut to estimate before you type, and compare the estimate with the converter result.
4. Use the exact factor from the converter whenever money, a cut, a dose, or a record depends on the answer.
5. Teach the shortcut by showing the friendly example, not by stating the factor alone, because the example is what memory keeps.

A second kind of shortcut is the doubling and halving family. Halving a quantity twice quarters it, doubling it twice quadruples it, and a ten percent shift is found by moving a decimal point. These moves combine with the table shortcuts: to convert a value that is not friendly, convert a nearby friendly value and adjust. For example, to estimate a distance a little over a friendly value, convert the friendly value, then add the conversion of the small remainder. The adjustment step keeps the estimate honest, and the habit of adjusting, rather than guessing the whole value at once, is what separates a useful estimate from a wild guess. Keep the converter open while you practice, and check every estimate until the estimates start landing close on their own.

Estimating and Sense Checking Before You Trust a Result

Estimating is not the opposite of calculating. It is the first half of calculating, and it earns its keep by catching the errors that exact arithmetic cannot catch, because arithmetic done with the wrong unit is still wrong. An estimate answers a simpler question: roughly how big should the answer be, and in which direction should it move? If the starting value is 60 and the target unit is larger, the answer should be smaller than 60. If the target unit is smaller, the answer should be larger. If the converter gives the opposite, the factor is upside down or the units are swapped, and no amount of decimal places will fix it. Hold that directional check in mind for every conversion, and you will catch the most damaging errors in seconds.

• Round the starting value to one or two friendly digits before you estimate.
• Apply a friendly factor, not the exact factor, and accept an answer within a few percent.
• Check direction first: larger target unit means a smaller number, smaller target unit means a larger number.
• Check size second: the answer should be in the same neighborhood as the estimate, not ten times larger or smaller.
• If the estimate and the converter disagree, recheck the From and To boxes before you recheck the arithmetic.
• Write the estimate beside the exact answer when the answer will be used by someone else, so they can see the reasoning.

Sense checking also means knowing when a number is too precise to be believed. A height converted to four decimal places in centimeters implies a measurement accurate to a hundredth of a millimeter, which no tape measure provides. A road distance quoted to six decimal places in kilometers implies a survey accurate to a millimeter over miles, which no odometer provides. When a result looks more precise than its input, trim the displayed digits to match the input, and the result becomes honest again. The decimal places control exists for exactly this judgment: it lets the display follow the measurement, rather than letting the calculator imply a precision the measurement never had. A result that is honest about its precision is more useful than a result that looks exact and is not.

Frequently Asked Questions

The questions below are the ones people ask most often about this kind of conversion, answered with the formula, the factor, and a worked example where one helps. If your question is not here, use the converter above with the value and units from your own task, and read the formula line: it answers most follow up questions by showing the factor that was applied.

How do I convert Fahrenheit to Celsius?

Subtract 32 from the Fahrenheit value, then multiply by 5 and divide by 9. For 68 degrees Fahrenheit, 68 minus 32 is 36, and 36 times 5 divided by 9 is 20, so the answer is 20 degrees Celsius. For 98.6 degrees Fahrenheit, 98.6 minus 32 is 66.6, and 66.6 times 5 divided by 9 is 37, which is normal body temperature. The subtraction matters: you cannot convert by multiplying alone, because the two scales start at different points.

How do I convert Celsius to Fahrenheit?

Multiply the Celsius value by 9, divide by 5, and add 32. For 20 degrees Celsius, 20 times 9 divided by 5 is 36, plus 32 is 68 degrees Fahrenheit. For 100 degrees Celsius, 100 times 9 divided by 5 is 180, plus 32 is 212 degrees Fahrenheit, the boiling point of water. For 0 degrees Celsius, the answer is 32 degrees Fahrenheit. A quick estimate is to double the Celsius value and add 32, then adjust: doubling is a little high for warm values, so the exact formula is worth using.

What is kelvin, and why does it have no degree sign?

Kelvin is the International System unit for thermodynamic temperature. It starts at absolute zero, the coldest possible temperature, and uses the same degree size as Celsius. Because kelvin is an absolute scale, its values are written as 293.15 K, not 293.15 degrees K. A change of one kelvin equals a change of one degree Celsius, but a temperature of 293.15 kelvin is 20 degrees Celsius, not 293.15 degrees Celsius. Kelvin is the scale used in physics and physical science whenever ratios of temperature matter.

What is absolute zero?

Absolute zero is 0 kelvin, which is minus 273.15 degrees Celsius and minus 459.67 degrees Fahrenheit. It is the lowest temperature that can exist in principle, the point at which molecular motion reaches its minimum. No temperature can go below it, and this converter will tell you if a value you enter would fall below it. In practice, scientists have cooled matter to tiny fractions of a kelvin above absolute zero, but reaching exactly zero is not possible. Everyday temperatures sit hundreds of kelvin above it.

At what temperature are Fahrenheit and Celsius equal?

The two scales are equal at minus 40. Minus 40 degrees Fahrenheit is minus 40 degrees Celsius. You can check it with either formula: (minus 40 minus 32) times 5 divided by 9 is minus 40, and minus 40 times 9 divided by 5 plus 32 is also minus 40. It is the only point where the numbers match. Above minus 40, Fahrenheit numbers are higher than Celsius numbers for the same temperature; below minus 40, Fahrenheit numbers are lower, because the Fahrenheit degree is smaller.

Why does the United States use Fahrenheit?

Fahrenheit was created in the early 1700s by Daniel Gabriel Fahrenheit, and it was the scale in common use in Britain and its colonies when the United States was founded. Weather reports, thermostats, ovens, and medical thermometers in the United States were all built around it, so it stayed in daily use. Most other countries adopted Celsius, which ties neatly to the freezing and boiling points of water. Science in the United States uses Celsius and kelvin, so Americans who travel, cook from foreign recipes, or study science switch scales often.

How do I convert a temperature difference, not a temperature?

A difference follows different rules from a temperature value, because the zero point offset cancels out. A rise of 10 degrees Celsius is a rise of 18 degrees Fahrenheit, since one Celsius degree is 1.8 Fahrenheit degrees. A rise of 10 kelvin is a rise of 10 degrees Celsius. Do not add 32 when you convert a difference: if a forecast says temperatures will rise by 10 degrees, convert only the size of the rise. To be safe, convert both endpoint temperatures with the full formula and subtract, which gives the same answer.

What temperature is considered a fever?

In Fahrenheit, a fever in an adult is usually defined as 100.4 degrees Fahrenheit or higher, which is 38 degrees Celsius. Normal body temperature is about 98.6 degrees Fahrenheit, or 37 degrees Celsius, but normal varies by person, by time of day, and by where the temperature is measured. A reading of 99 degrees Fahrenheit is often just a normal variation. Always follow the guidance of a health professional for a child, an older adult, or a fever that lasts more than a few days, and use the same thermometer type for comparisons.

Can kelvin be negative?

No. Kelvin starts at absolute zero, so kelvin values are zero or positive. A value below 0 kelvin has no physical meaning. Celsius and Fahrenheit can be negative, because their zero points sit well above absolute zero: minus 10 degrees Celsius is 263.15 kelvin, and minus 10 degrees Fahrenheit is 249.82 kelvin. If you enter a kelvin value below zero, or a Celsius value below minus 273.15, this converter explains the problem instead of returning a meaningless number.

What is the formula for every pair of scales?

There are six conversions, and all of them pass through Celsius. Fahrenheit to Celsius: (F minus 32) times 5 divided by 9. Celsius to Fahrenheit: C times 9 divided by 5, plus 32. Celsius to kelvin: C plus 273.15. Kelvin to Celsius: K minus 273.15. Fahrenheit to kelvin: (F minus 32) times 5 divided by 9, plus 273.15. Kelvin to Fahrenheit: (K minus 273.15) times 9 divided by 5, plus 32. Learn the first two and the 273.15 offset, and the other four follow.

Disclaimer: This converter is for general information and everyday calculation only. Conversion factors are exact as defined, but measurements, labels, and records should be checked against the original source before they are used for a purchase, a cut, a shipment, a medical decision, or a legal matter. When precision matters, verify the value with a calibrated instrument or an official record.