MPG Calculator — Gas Mileage & Trip Fuel Cost

Work out your miles per gallon, plan a road trip, and see exactly what the drive will cost. This free MPG calculator covers both jobs: measure your car’s real fuel economy from a fill-up, or plan a trip with your MPG, the local gas price, a round-trip toggle, and a cost split between passengers. It also works out your monthly commute cost, compares gas with electric driving, and estimates the CO2 your trip puts out — all instantly, right in your browser, with US gallons throughout.

What Is MPG?

MPG stands for miles per gallon, and it is the number Americans use to describe how far a car travels on one gallon of fuel. A car rated at 28 MPG goes 28 miles on a single gallon of gasoline. A car rated at 45 MPG goes 45 miles on that same gallon, which means it uses roughly a third less fuel for the same trip. The higher the number, the less fuel you burn, the less you pay at the pump, and the less carbon dioxide comes out of the tailpipe.

MPG is a measure of fuel economy, not of speed or power. Two cars can have the same engine size and very different MPG, because weight, shape, tyres, gearing, and driving style all change how efficiently fuel turns into motion. A light, aerodynamic hybrid sips fuel; a heavy pickup with a big engine and the aerodynamics of a brick does not. That is why the official ratings on fueleconomy.gov, the US government fuel economy site, list separate city, highway, and combined figures for every new car sold in the United States.

For most drivers, MPG matters for three practical reasons. First, it decides what a trip costs: at 28 MPG and $4.15 a gallon, a 300-mile drive needs 10.71 gallons and costs $44.46 in fuel. Second, it decides the monthly budget: the same car driven 25 miles each way to work, 22 days a month, costs about $154.00 a month in fuel at 25 MPG and $3.50 a gallon. Third, it is the simplest way to compare cars before you buy one, because a 5 MPG difference is worth hundreds of dollars a year for a typical driver.

Why MPG Matters More Than Tank Size

A big tank feels reassuring, but it is MPG that decides how often you stop. A pickup with a 26-gallon tank at 20 MPG travels about 520 miles before it is empty. A hybrid with a 12-gallon tank at 45 MPG travels about 540 miles — further, on less than half the fuel. Tank size decides the size of the bill at each fill-up; MPG decides how many bills you get. When you compare cars, look at the combined MPG first and treat tank size as a convenience, not an economy figure.

US Gallon vs Imperial Gallon

Every number on this page uses the US gallon, which is 3.78541 litres. The imperial gallon used in the United Kingdom is larger, at 4.54609 litres, so a car that scores 40 MPG in the UK would score only about 33 MPG on the US scale — the same car, the same fuel, a different gallon. If you ever read a British review or a Canadian figure from before metrication, divide the imperial MPG by 1.20095 to get the US number. The calculator above, and every table below, is in US gallons unless it says otherwise.

How to Calculate MPG: The Tank-Fill Method

The honest way to find your real MPG is the tank-fill method, and it needs nothing more than your odometer and a gas station. Fill the tank completely and write down the odometer reading, or reset the trip meter to zero. Drive normally until the tank is low, then fill up completely again and write down how many gallons went in and how many miles you drove since the last fill-up. Divide the miles by the gallons, and you have your MPG for that tank.

The formula is simple: MPG equals miles driven divided by gallons used. Drive 350 miles and add 14 gallons at the pump, and your MPG is 350 divided by 14, which is 25.0 MPG. The same 25 MPG converts to 10.63 kilometres per litre (multiply by 0.425144) and 9.41 litres per 100 kilometres (divide 235.215 by the MPG). Those are the figures the rest of the world uses, and the calculator shows all three so you can compare with foreign reviews and rental cars abroad.

One fill-up is noisy. A pump may click off early, a hill-heavy week may skew the result, and a cold snap makes engines thirstier. Measure over three or four fill-ups and average the results, and the number settles down to something you can trust. Keep a small log — date, miles, gallons — and after a month you will know your car better than the window sticker does.

The Tank-Fill Method, Step by Step

1. Fill the tank until the pump clicks off, then stop. Do not top it off.
2. Record the odometer reading, or reset the trip meter to zero.
3. Drive normally for at least half a tank, ideally a full tank.
4. Fill up completely again at the same station if you can, and note the gallons added.
5. Divide the miles driven by the gallons added. That is your MPG for that tank.
6. Repeat for three or four tanks and average the results for a reliable figure.

Why Your Real MPG Differs From the Sticker

The official EPA rating is measured in a laboratory on a standard driving cycle, and real life is messier. Short trips hurt the most, because a cold engine burns extra fuel for the first few miles. Air conditioning, roof boxes, under-inflated tyres, and a heavy foot all pull the number down. Winter petrol blends, cold air, and stop-and-go traffic do the same. Most drivers see 10 to 20 percent less than the combined EPA figure in everyday driving, and that is normal — it is a sign that the rating is a comparison tool, not a promise.

How to Use This MPG Calculator

The calculator has two modes, and you can switch between them at any time. Trip Cost is the default mode: enter the distance, your car’s MPG, the gas price where you fill up, and how many people are splitting the cost, and it works out the gallons, the total cost, the cost per mile, the cost per person, the round-trip cost, and the CO2. Tick the round-trip box and the distance doubles automatically. My MPG is the measuring mode: enter the miles you drove and the gallons you added, and it gives you your MPG plus the metric equivalents and the cost per mile at your gas price.

Below the main result, two extra sections run on the same numbers. The commute section turns a one-way distance and a number of working days into a monthly and annual fuel cost. The gas-versus-electric section compares the same trip in a petrol car and in an EV, using miles per kilowatt-hour and your electricity price. Everything updates as you type, and nothing you enter leaves your browser.

Trip Cost Mode

• Trip distance: the one-way distance in miles. Use the length converter if your route is measured in kilometres.
• Vehicle MPG: your car’s combined MPG, or tap a preset — hybrid 45, sedan 30, SUV 25, pickup 20.
• Gas price: the price per gallon at your local station, not the national average.
• People splitting the cost: the number of passengers sharing the fuel bill.
• Round trip: tick this when you are driving there and back, and the maths doubles the distance.

My MPG Mode

• Miles driven: the distance since the last full tank, from the odometer or trip meter.
• Gallons used: the gallons added at this fill-up, from the pump receipt.
• Gas price: optional, but it adds the cost per mile to your result.
• Tank size: optional, and it adds your range on a full tank.

Worked Examples

Three examples show the maths the calculator does, so you can check any result by hand. Each one uses the same formulas: gallons equal miles divided by MPG, trip cost equals gallons times price, and cost per mile equals price divided by MPG.

Example 1 — A Short Trip

Drive 100 miles in a car that gets 25 MPG, with gas at $3.50 a gallon. Gallons needed are 100 divided by 25, which is 4.00 gallons. Trip cost is 4.00 times $3.50, which is $14.00. Cost per mile is $3.50 divided by 25, which is $0.14. A hundred miles for fourteen dollars is the kind of number that makes a 25 MPG car feel cheap on short hops, and it is also why a small improvement in MPG shows up fast on a long commute.

Example 2 — A Longer Drive

Drive 340 miles at 28.5 MPG, with gas at $3.55 a gallon. Gallons needed are 340 divided by 28.5, which is 11.93 gallons. Trip cost is 11.93 times $3.55, which is $42.35. Cost per mile is $3.55 divided by 28.5, which is about $0.12. This is a typical interstate day trip: just under twelve gallons, a little over forty-two dollars, and a per-mile fuel cost of twelve cents.

Example 3 — The Monthly Commute

Commute 25 miles each way, 22 working days a month, in a car that gets 25 MPG, with gas at $3.50 a gallon. Cost per mile is $3.50 divided by 25, which is $0.14. The daily round trip is 50 miles, so the daily fuel cost is 50 times $0.14, which is $7.00. The monthly cost is $7.00 times 22 days, which is $154.00, and the annual cost is $154.00 times 12, which is $1,848.00. That annual figure is the one worth staring at: nearly two thousand dollars a year just to get to work and back, before insurance, maintenance, or the car payment.

The Default Trip, Checked by Hand

The calculator opens on a 300-mile trip at 28 MPG and $4.15 a gallon. Gallons are 300 divided by 28, which is 10.71. Trip cost is 10.71 times $4.15, which is $44.46. Cost per mile is $4.15 divided by 28, which is $0.15. A round trip doubles the cost to $88.93, and four people splitting the one-way cost pay $11.12 each. Every number in the result box follows from those three divisions, and you can reproduce all of them on a pocket calculator.

Typical MPG by Vehicle Type

Not every car is built to sip fuel, and the spread between vehicle types is wide. A hybrid can travel twice as far on a gallon as a pickup truck, which is why the vehicle you drive matters more than any driving tip. The table below gives typical combined MPG ranges for the main vehicle types sold in the United States in 2026. Individual models vary — a small turbo sedan can beat a large hybrid, and a heavy SUV with a V8 can fall below the pickup range — so use these as starting points and check the exact rating for your model on fueleconomy.gov.

The trip-cost column uses the same maths as the calculator: gallons equal 300 divided by MPG, and cost equals gallons times $4.15. A hybrid at 45 MPG needs 6.67 gallons and costs $27.67 for the same 300 miles that costs a 20 MPG pickup $62.25 — a difference of $34.58 on a single trip, and thousands over a year of driving. That gap is the whole economic case for a hybrid or an efficient sedan, and it is why the calculator includes vehicle presets: tap one, and the result updates instantly.

Electric cars do not have an MPG at all, so they are rated in miles per kilowatt-hour or in MPGe, a miles-per-gallon-equivalent that converts electricity into the energy of a gallon of gasoline. A typical EV manages about 3.5 miles per kWh, which at $0.17 per kWh works out to roughly $0.05 a mile — about a third of the fuel cost of a 28 MPG gas car at $4.15 a gallon. The comparison section of the calculator runs that maths for your exact trip.

US Gas Prices in 2026

Gas prices are local, and the national average is only a starting point. According to the US Energy Information Administration’s Gasoline and Diesel Fuel Update, the US average for regular gasoline was $4.153 a gallon on November 2, 2026, with AAA reporting $4.149 the same week. The 2026 weekly peak was $4.50, reached on May 11, 2026, and the EIA’s October 2026 Short-Term Energy Outlook forecast an average of $3.91 a gallon for 2026 as a whole. Those are averages, and the spread between states is large: California averaged $5.748 the same week the East Coast averaged $3.936 — a difference of about $1.80 a gallon for the same fuel.

That spread changes trip maths dramatically. A 300-mile trip at 28 MPG needs 10.71 gallons, which costs $42.16 on the East Coast at $3.936, $44.46 at the national average of $4.15, and $61.59 in California at $5.748. Same car, same distance, nearly twenty dollars apart. Always enter your local price in the calculator, and never plan a trip on the national average — check the price where you will actually fill up, using the EIA Gasoline and Diesel Fuel Update, which publishes the weekly survey behind these figures.

Why Gas Prices Vary So Much

• State taxes: state fuel taxes differ by more than fifty cents a gallon between the cheapest and most expensive states.
• Reformulated petrol: California and some metro areas require cleaner-burning blends that cost more to refine.
• Distance from refineries: fuel trucked a long way from a refinery or port carries the transport cost in the price.
• Seasonal blends: summer petrol is blended differently from winter petrol and usually costs more.
• Crude oil prices: the world oil price is the biggest single input, and it moves with global supply, demand, and disruption.
• Local competition: a town with several stations on one corner usually has lower prices than a town with one station on a highway exit.

What Moves the Price Week to Week

Most of the week-to-week movement comes from crude oil, which reacts to OPEC decisions, refinery outages, hurricanes in the Gulf of Mexico, and shifts in demand. Refinery maintenance in spring and autumn can push prices up for a few weeks, and the switch to summer blend in late spring is a regular seasonal rise. The EIA forecast of $3.91 for 2026 as a whole sits below the November weekly figure, which is a reminder that a single week’s price is a snapshot, not a trend. For trip planning, the price at your station this week is the only number that matters.

What a Trip Costs at Different Gas Prices

The table below holds the trip and the car constant — 300 miles at 28 MPG — and changes only the gas price. It shows how sensitive a trip is to the price at the pump, and why a few cents a gallon matters more on a long drive than on a short one. Every figure follows the same two steps: gallons equal 300 divided by 28, which is 10.71, and cost equals 10.71 times the price.

A dollar a gallon, from $3.00 to $4.00, adds about $10.71 to this trip — the price of the gallons themselves, since the gallons do not change. Over a year of driving 12,000 miles at 28 MPG, that same dollar a gallon is worth about $428.57, which is why fuel economy and fuel price deserve equal attention in a household budget. If your car gets 20 MPG instead of 28, the same 12,000 miles need 600 gallons instead of 428.57, and at $4.15 a gallon the annual fuel bill rises from $1,778.57 to $2,490.00 — a difference of $711.43 a year, every year, for the same driving.

Trip Cost, Step by Step

Planning a trip’s fuel cost takes four numbers and three divisions, and the calculator does all of it, but it helps to know the steps. First, find the distance — use a maps app for the real route, not the straight-line distance, because the route is always longer. Second, use your car’s real MPG from the tank-fill method, not the window sticker, because the real number is what you will actually burn. Third, use the gas price where you will fill up, which may be different at the start and the end of the trip. Fourth, decide whether the cost is split, and by how many people.

Then the maths: gallons equal distance divided by MPG, total cost equals gallons times price, and cost per mile equals price divided by MPG. Cost per mile is the most useful of the three, because it lets you compare any two trips instantly — a 300-mile trip at $0.15 a mile costs $45.00 in fuel, and a 500-mile trip at the same rate costs $75.00. It also lets you compare cars: at $4.15 a gallon, a 28 MPG car costs $0.15 a mile in fuel, a 20 MPG pickup costs $0.21 a mile, and a 45 MPG hybrid costs $0.09 a mile.

Round Trips and Return Journeys

Tick the round-trip box and the calculator doubles the distance before doing the maths. A 300-mile one-way trip at 28 MPG and $4.15 costs $44.46; the round trip is 600 miles, needs 21.43 gallons, and costs $88.93. Remember that the return journey is rarely identical: traffic, elevation, and wind can change the MPG on the way back, and the gas price at the destination may differ from the price at home. For a long trip, fill up where fuel is cheapest and plan the return leg with the destination price.

Splitting the Cost Fairly

Four people sharing a $44.46 trip pay $11.12 each, which is the calculator’s default split example. The fair split is the fuel cost divided by the number of people, and it works for any group size — but agree it before the trip, not after. If one person drives their own car and the others ride along, the driver is also paying the wear on the car, so some groups add a small amount per mile for the driver. The IRS standard mileage rate covers all driving costs, not just fuel, and it is a separate concept from the fuel-only cost this calculator shows — do not mix the two when you split a bill.

Your Daily Commute: Monthly and Annual Fuel Cost

The commute is where fuel cost hides, because a small daily number becomes a large monthly one. The formula is simple: monthly cost equals one-way miles times two, times working days, times cost per mile. Cost per mile is the gas price divided by MPG, so the whole calculation rests on two numbers you already know. The table below uses 25 MPG and $3.50 a gallon, which gives a cost per mile of $0.14, and 22 working days a month — a standard full-time month with weekends off.

A 25-mile commute costs $154.00 a month and $1,848.00 a year in fuel alone, and a 40-mile commute costs $246.40 a month and $2,956.80 a year. Those are fuel-only figures, before insurance, tyres, maintenance, depreciation, and tolls. The commute section of the calculator runs the same maths with your own numbers — change the distance, the days, the MPG, or the price, and the monthly and annual figures update at once. If you are weighing a move closer to work or a more efficient car, this is the number to compare: a 10 MPG improvement on a 25-mile commute at $3.50 a gallon saves about $44.00 a month, or about $528.00 a year.

Working from home changes the maths completely. Two remote days a week cut a five-day commute to three days, which cuts the fuel bill by 40 percent — on the 25-mile example, from $154.00 to $92.40 a month. Carpooling does the same thing in a different way: two people sharing the drive halve the cost each, and four people quarter it. The cheapest mile is always the one you do not drive, and the second cheapest is the one you share.

How the Commute Adds Up Over a Career

Multiply the annual figure by the years you expect to keep the same commute, and the scale becomes hard to ignore. Ten years at $1,848.00 a year is $18,480.00 in fuel — more than the price of a good used car — and that assumes gas stays at $3.50, which it will not. A shorter commute or a more efficient car is not a small saving; it is one of the largest levers in a household budget, and it is worth weighing against housing costs when you choose where to live. See what a fuel saving is worth over time with the compound interest calculator, and how it fits a monthly budget with the salary calculator.

Cost Per Mile: What It Covers and What It Does Not

Cost per mile in this calculator is fuel only: gas price divided by MPG. At $4.15 a gallon and 28 MPG, it is $0.15 a mile. That number is useful for comparing cars and planning trips, but it is not the full cost of driving. The full cost adds insurance, depreciation, maintenance, tyres, registration, and tolls, and for most cars the full cost per mile is three to four times the fuel-only figure. A car that costs $0.15 a mile in fuel may cost $0.60 a mile all in, and the difference is mostly depreciation and insurance, which you pay whether you drive or not.

The IRS standard mileage rate is a separate concept again. It is a single rate the US tax authority publishes each year for business driving, and it covers all driving costs — fuel, wear, insurance, depreciation — in one number. It is not a fuel price, and it should not be used to split a road-trip fuel bill. If you are reimbursed for business miles, use the IRS rate; if you are splitting fuel with friends, use the fuel-only cost from this calculator.

What Else a Mile Costs

• Depreciation: the largest single cost for a newer car, and it grows with miles driven.
• Insurance: mostly fixed, but some insurers price by annual mileage.
• Maintenance: oil, filters, brakes, and tyres all wear by the mile.
• Registration and taxes: annual, and mostly unrelated to miles.
• Tolls and parking: route-dependent, and often larger than the fuel on a city trip.

When Fuel-Only Is the Right Number

Fuel-only cost per mile is the right number when the car already exists and the question is whether to drive it somewhere — a road trip, a commute, a delivery run. The fixed costs are already paid, so the extra cost of the trip is the fuel, plus tolls. It is the wrong number when you are deciding whether to own a car at all, or comparing owning with renting, ridesharing, or public transport, because then the fixed costs count too.

Gas Car vs Electric Car: A Fair Comparison

The calculator’s comparison section puts a gas car and an EV over the same trip, using the same distance. The default trip is 300 miles. The gas car at 28 MPG and $4.15 a gallon needs 10.71 gallons and costs $44.46. The EV at 3.5 miles per kWh and $0.17 per kWh needs 85.71 kWh and costs $14.57. The EV saves $29.89 on this trip — about two-thirds less in fuel cost. That is a typical gap at current US prices, and it is why fuel cost is the strongest economic argument for an EV.

Over 12,000 miles a year, the gas car costs $1,778.57 in fuel and the EV costs $582.86 in electricity, a saving of $1,195.71 a year. Those figures use the calculator’s defaults, and your own numbers will differ — electricity prices vary by state and by time of day, home charging is usually cheaper than public fast charging, and cold weather cuts EV efficiency. But the shape of the answer is stable: at typical US prices, an EV’s energy costs roughly a third of a gas car’s fuel costs per mile.

The fair comparison also counts what is not in the table. EVs have no oil changes and fewer moving parts, but they cost more to buy, tyres can wear faster because of the weight, and home charging needs a place to plug in. Gas cars are cheaper to buy and refuel anywhere in five minutes, but they need more maintenance and their fuel price moves with the oil market. Fuel cost alone favours the EV; the full decision weighs purchase price, charging access, and how far you drive.

MPGe, Explained

Because an EV uses no gallons, the EPA rates it in MPGe — miles per gallon equivalent — by converting electricity into the energy content of a gallon of gasoline, which is 33.7 kWh. An EV that travels 3.5 miles per kWh is rated at about 118 MPGe, because 3.5 times 33.7 is 117.95. MPGe is a useful comparison on a window sticker, but it is not a cost figure: a high MPGe does not tell you what a mile costs, because electricity and gasoline have different prices. For cost, use miles per kWh and your electricity rate, exactly as the calculator does.

CO2 Emissions From Your Tank

Burning a gallon of gasoline releases 8.887 kilograms of carbon dioxide, according to the US Environmental Protection Agency. That figure is for gasoline only — diesel is different, at about 10.180 kilograms per gallon — and it counts only the CO2 from burning the fuel, not the emissions from extracting, refining, and transporting it. The calculator multiplies your gallons by 8.887 to give the trip’s CO2, so the default 300-mile trip at 28 MPG, which needs 10.71 gallons, emits 95.2 kilograms of CO2.

A typical American car emits about 4.6 metric tons of CO2 a year, which is 4,600 kilograms — roughly 518 gallons of gasoline at 8.887 kilograms each. Improving MPG cuts that directly: at 12,000 miles a year, a 20 MPG car burns 600 gallons and emits 5,332.2 kilograms, while a 28 MPG car burns 428.57 gallons and emits 3,808.7 kilograms, a saving of 1,523.5 kilograms a year. A 45 MPG hybrid burns 266.67 gallons and emits 2,369.9 kilograms, saving 2,962.3 kilograms against the pickup. These are tailpipe figures, and they are the reason fuel economy standards exist: every gallon not burned is 8.887 kilograms not emitted.

The comparisons in the last column are rough illustrations, not precise equivalences, because flights, home electricity, and driving all have different emission profiles. The point is scale: a single long road trip emits on the order of a hundred kilograms, and a year of driving emits on the order of tonnes. If you want to cut it, the levers in order are driving less, driving a more efficient car, and driving an EV charged on clean electricity.

MPG, km/L and L/100km: Converting Between Systems

The United States measures fuel economy in miles per gallon, and almost everywhere else measures it in litres per 100 kilometres — which runs the other way round, because a lower L/100km number means better economy. Kilometres per litre sits in between and runs the same way as MPG: higher is better. The calculator shows all three, and the table below lists the conversions for the MPG values you are most likely to meet.

The formulas are: km/L equals MPG times 0.425144, L/100km equals 235.215 divided by MPG, and gallons per 100 miles equals 100 divided by MPG. Gallons per 100 miles is worth knowing even in the US, because it shows fuel use directly: a 20 MPG car uses 5.00 gallons every 100 miles, a 25 MPG car uses 4.00, and a 50 MPG car uses 2.00. The jump from 20 to 25 MPG saves a full gallon per hundred miles, while the jump from 40 to 50 MPG saves only half a gallon — the same 5 MPG improvement is worth far more at the low end, which is why replacing the thirstiest car in a household saves more fuel than squeezing a few more MPG out of an already efficient one.

If you rent a car abroad, the dashboard will show L/100km, and the table above is your translation. A rental showing 7.84 L/100km is a 30 MPG car in American terms — respectable. A rental showing 11.76 L/100km is a 20 MPG car — thirsty. And if you buy fuel by the litre, remember that a US gallon is 3.78541 litres, so a price of $1.10 a litre is about $4.16 a gallon.

How to Improve Your MPG

Most drivers can gain 10 to 20 percent in fuel economy without spending money, because the biggest losses come from driving style and maintenance, not from the car itself. The gains below are the ones the EPA and fueleconomy.gov list as the most reliable, and they stack: a gentle foot plus correct tyre pressure plus a lighter load can easily move a car from 25 MPG to 28 or 29 MPG, which on 12,000 miles a year at $4.15 a gallon saves about $213.00 to $275.00 a year.

Driving Habits That Save Fuel

• Slow down on the highway: fuel economy drops sharply above 50 mph, and every 5 mph over 50 is like paying an extra $0.30 or more per gallon.
• Accelerate gently: jackrabbit starts waste fuel; smooth, gradual acceleration keeps the engine in its efficient range.
• Anticipate stops: lifting off early and coasting to a red light beats braking late, and it saves brake wear too.
• Use cruise control: a steady speed on the highway beats the small speed changes of a human foot.
• Avoid idling: idling burns fuel for zero miles, so turn the engine off if you will wait more than a minute.
• Combine trips: a cold engine is thirsty, so several short trips from one warm start beat the same trips spread across the day.

Maintenance That Pays for Itself

• Tyre pressure: under-inflated tyres raise rolling resistance; check monthly and keep them at the pressure on the door sticker, not the tyre sidewall.
• Air filter: a clogged filter chokes the engine; replace it on schedule.
• Engine oil: use the grade the manufacturer recommends, because the wrong viscosity adds friction.
• Wheel alignment: a car that pulls to one side scrubs its tyres and wastes fuel.
• Roof racks and boxes: remove them when not in use, because they add drag at highway speed.
• Extra weight: every 100 pounds of cargo costs roughly 1 to 2 percent in MPG, so clear the trunk — and if you are weighing gear in kilograms, the weight converter turns it into pounds and back.

What Does Not Help Much

Fuel additives, magnets, and miracle devices sold online do not improve MPG in any test the EPA has run — save the money. Premium petrol in a car designed for regular does nothing either, because the octane rating is about knock resistance, not energy. And warming the car up for ten minutes on a winter morning burns fuel for zero miles; modern engines warm up faster under light driving than they do idling in the driveway. The honest gains are boring: drive gently, keep the tyres up, and carry less weight.

Common MPG Mistakes

Most MPG errors come from the same few misunderstandings, and they are easy to avoid once you know them. The calculator is built to sidestep them — US gallons throughout, cost per mile labelled as fuel only, and the tank-fill method explained rather than assumed — but the list below is worth reading before you trust any MPG number, including one from this page.

• Mixing US and imperial gallons: an imperial gallon is 20 percent larger, so a UK MPG figure looks 20 percent better than the same car on US gallons. Always check which gallon the number uses.
• Trusting one fill-up: a pump that clicks off early makes the MPG look better than it is; average several tanks.
• Using the sticker as your real MPG: the EPA combined figure is a comparison tool, and real driving usually lands 10 to 20 percent below it.
• Planning on the national average gas price: California and the East Coast differed by about $1.80 a gallon in November 2026 — use your local price.
• Counting cost per mile as the full cost of driving: fuel-only cost per mile excludes insurance, depreciation, and maintenance, which are the larger share.
• Forgetting the return journey: a one-way distance is half the trip; tick the round-trip box or double the miles yourself.
• Comparing MPG across fuel types: diesel, gasoline, and electricity have different energy contents, so compare cost per mile instead of raw MPG.
• Assuming a bigger tank means better economy: tank size decides how far you go between fill-ups; MPG decides how much fuel that distance needs.

Frequently Asked Questions

What is a good MPG for a car in the US?

About 28 MPG combined is a reasonable reference point for a modern car in the United States, according to EPA and fueleconomy.gov data. A sedan at 28 to 32 MPG is normal, an SUV at 22 to 28 MPG is normal, and a hybrid at 40 to 50 MPG is good. Anything above 35 MPG combined is efficient by US standards, and anything below 20 MPG is thirsty unless the vehicle is a heavy truck doing truck work.

How do I calculate MPG from a fill-up?

Fill the tank completely, note the odometer reading, drive until the tank is low, then fill up completely again. Divide the miles driven by the gallons added at the second fill-up. For example, 350 miles and 14 gallons gives 25.0 MPG. Repeat over several tanks and average the results for a reliable figure.

How much does a 300-mile trip cost in gas?

It depends on your MPG and the local gas price. At 28 MPG and $4.15 a gallon, a 300-mile trip needs 10.71 gallons and costs $44.46. At 25 MPG and $3.50 a gallon, the same trip needs 12.00 gallons and costs $42.00. Enter your own numbers in the calculator above for the exact figure.

What is the difference between MPG and MPGe?

MPG measures miles per gallon of gasoline. MPGe, miles per gallon equivalent, rates electric cars by converting electricity into the energy of a gallon of gasoline, which is 33.7 kWh. An EV at 3.5 miles per kWh is rated at about 118 MPGe. MPGe compares efficiency, but it does not tell you the cost per mile — for that, use your electricity price and miles per kWh.

Does air conditioning hurt MPG?

Yes, but less than most people think at highway speed. Air conditioning can cut MPG by roughly 5 to 10 percent in city driving and less on the highway, where open windows add drag that can cost more than the air conditioning. At low speed, windows down is cheaper; at highway speed, air conditioning with the windows closed is usually the more efficient choice.

How accurate is this MPG calculator?

The maths is exact for the numbers you enter — gallons equal miles divided by MPG, and cost equals gallons times price. The accuracy of the answer depends on the accuracy of your inputs, especially your real MPG and your local gas price. Measure MPG over several fill-ups and use the price at the station where you will fill up, and the result will be as accurate as the inputs allow.

Why is my MPG lower in winter?

Cold air is denser, which adds drag; engines take longer to warm up, and a cold engine burns more fuel; winter petrol blends contain slightly less energy; and short trips suffer most, because the engine may never reach full temperature. Tyre pressure also drops in the cold, which adds rolling resistance. A 10 to 15 percent winter drop is normal, and it recovers in spring.

Disclaimer: This calculator is for general information only and is not financial advice. Gas prices, fuel economy ratings, and CO2 factors change over time, and your actual fuel use depends on your vehicle, driving conditions, and local fuel price. The EIA average gas price quoted here is context only — always use the price at your local station. Talk to a qualified mechanic or dealer about your vehicle’s fuel economy, and to a financial adviser about vehicle purchase decisions.