What Is My BMI?
If you are asking “what is my BMI?”, the answer is one number away. Enter your height and weight in the BMI calculator above and you will see your BMI, your category, your healthy weight range, and two extra numbers — BMI prime and ponderal index — instantly. This page explains what that number means, whether it is healthy, and what to do about it.
BMI stands for Body Mass Index. It is a simple ratio of your weight to your height, used by doctors and health organisations around the world as a quick screening tool. It does not measure body fat directly, and it cannot tell muscle apart from fat — but as a first check of whether your weight is in a healthy range, it is fast, free, and widely used.
How to Find Your BMI in 30 Seconds
Finding your BMI takes three quick steps. First, weigh yourself in the morning, in light clothing and no shoes, on a hard floor. Second, measure your height barefoot against a wall. Third, enter both numbers in the calculator above — or work it out by hand with the formula BMI = weight (kg) ÷ height (m)². For example, 70 kg at 1.75 m gives 70 ÷ 3.0625 = 22.9.
If you use pounds and inches, the formula is BMI = 703 × weight (lb) ÷ height (in)². A person at 154 lb and 5 feet 9 inches works out as 703 × 154 ÷ 69² = 22.7. The calculator above handles both unit systems — switch with the Metric and Imperial buttons and it converts for you. The detailed steps, including how to avoid the common measuring errors, are explained in the worked examples on the BMI calculator page.
- Weigh yourself. Morning, after the bathroom, before breakfast, same scale, hard floor.
- Measure your height. Barefoot, heels together, back to the wall, looking straight ahead.
- Enter both numbers. The calculator shows your BMI, your category, and your healthy weight range instantly.
- Read the category, not just the number. The band you fall in matters more than the decimal.
What the Number Means
Your BMI places you in one of the World Health Organization bands. The healthy band runs from 18.5 to 24.9. Below it you are underweight; above it you are overweight, then obese in three classes. The bands are conventions for population statistics, not cliffs in your body — the risk at 25.0 is only slightly above the risk at 24.9 — but they are the standard every doctor uses as a first check. The World Health Organization’s obesity fact sheet explains how these bands are used worldwide.
| Your BMI | Category | What it means for you |
|---|---|---|
| Below 18.5 | Underweight | Below the healthy range; possible nutritional deficiency and bone loss |
| 18.5 – 24.9 | Healthy weight | Range linked to the lowest health risks |
| 25.0 – 29.9 | Overweight | Modestly raised risk of heart disease and type 2 diabetes |
| 30.0 – 34.9 | Obese (Class I) | Substantially raised metabolic risk |
| 35.0 – 39.9 | Obese (Class II) | High risk; often qualifies for weight-loss support |
| 40.0 and above | Obese (Class III) | Very high risk; medical guidance recommended |
Two extra numbers in your result are worth knowing. BMI prime is your BMI divided by 25, the top of the healthy range. For the default example on this page — 70 kg at 175 cm, BMI 22.9 — the prime is 0.91, which means you sit 9 percent below the healthy ceiling. The ponderal index divides weight by height cubed instead of squared, which makes it steadier for very short or very tall people; for the same example it is 13.1.
Is My BMI Healthy?
A BMI between 18.5 and 24.9 is considered healthy for most adults. But “healthy” is a band, not a single number, and where you sit inside the band matters less than whether you are inside it at all. A BMI of 19.6 and a BMI of 24.0 are both healthy, and neither is meaningfully better than the other on its own. What matters more is the trend over months, and the other numbers alongside it — waist size, blood pressure, blood sugar, and fitness.
Your healthy weight range depends on your height. The table below shows the weight range that keeps BMI between 18.5 and 24.9 for common adult heights. Find your height and you have a sensible target zone without doing any maths.
| Height | Healthy weight range (BMI 18.5 – 24.9) |
|---|---|
| 150 cm (4 ft 11 in) | 41.6 – 56.0 kg |
| 160 cm (5 ft 3 in) | 47.4 – 63.7 kg |
| 170 cm (5 ft 7 in) | 53.5 – 72.0 kg |
| 175 cm (5 ft 9 in) | 56.7 – 76.3 kg |
| 180 cm (5 ft 11 in) | 59.9 – 80.7 kg |
| 190 cm (6 ft 3 in) | 66.8 – 89.9 kg |
If your weight is inside the range for your height, your BMI is healthy. If it is outside, the distance to the nearest edge of the range is the amount to aim for — for example, a person at 170 cm weighing 90 kg is 18.0 kg above the top of the range (72.0 kg), and their BMI is 31.1. Even the first 5 to 10 percent of body weight lost — 4.5 to 9 kg for that person — measurably improves blood pressure, blood sugar, and joint load.
What If My BMI Is Too High?
A BMI above 25.0 is a prompt to act, not a verdict. The most reliable first steps are unglamorous: eat slightly less than you burn, walk daily, and sleep well. Find your daily calorie needs with the calorie calculator, then eat 250 to 500 kcal below maintenance. Add a 30-minute walk every day and two short strength sessions a week to protect muscle while fat comes off. Recheck your BMI monthly, comparing weekly average weights rather than single readings.
If your BMI is 30.0 or higher, involve your doctor as well, especially if you have high blood pressure, high blood sugar, sleep apnoea, or joint pain. A plan built with a clinician — which may include diet support, activity coaching, or medication — beats a plan built alone.
What If My BMI Is Too Low?
A BMI below 18.5 carries its own risks, including nutritional deficiency, bone loss, and reduced immune function. If you are trying to gain weight, add calorie-dense foods such as nuts, oils, and dairy, eat more often, and add strength training so the gain is muscle as well as fat. If the low weight is unintentional — you are losing weight without trying — see a doctor, because unexplained weight loss needs checking. Your BMR tells you the calories your body burns at rest, which is the floor any weight-gain plan must exceed.
BMI for Men vs Women
The formula is identical for men and women, and the categories are the same for both sexes. But women naturally carry a higher body fat percentage at the same BMI, and the health meaning of a given number differs slightly. A woman with a BMI of 24 and a man with a BMI of 24 can have quite different body compositions, which is why interpretation should account for body composition rather than the number alone.
- Women: at the same BMI, women typically carry about 10 percent more body fat than men, and store more of it on the hips and thighs, which carries lower risk than abdominal fat.
- Men: men store more fat around the abdomen, so a high BMI in a man more often comes with a large waist — and waist size above 94 cm (37 inches) means increased risk, above 102 cm (40 inches) substantially increased risk.
- Waist matters for both: for women, a waist over 80 cm (31.5 inches) means increased risk and over 88 cm (35 inches) substantially increased risk.
- Muscle changes the reading: a man who lifts weights can score overweight with very little body fat, and the same is true for athletic women. Check body fat percentage before acting on the number.
BMI by Age
The adult cut-offs do not change with age — the healthy band is 18.5 to 24.9 at 25 and at 65. But how you read the number changes, because bodies change. Muscle is gradually replaced by fat with age, so an older person can sit inside the healthy BMI band while carrying an unhealthy amount of fat. Several large studies have found that slightly higher BMIs, up to around 27, are linked with lower mortality in people over 65 — sometimes called the obesity paradox — though it is debated, and the practical lesson is to read BMI alongside strength, mobility, waist size, and body composition, not on its own.
| Age group | How to read your BMI |
|---|---|
| 20 – 39 | Standard bands apply cleanly; muscle mass is usually highest, so check body fat if you train |
| 40 – 49 | Same bands; metabolism and muscle start to shift, so waist size deserves as much attention as weight |
| 50 – 64 | Same bands; fat tends to move to the abdomen, so a waist check matters more than the number alone |
| 65 and over | Same bands, but a BMI up to around 27 is often less concerning than at younger ages; strength and mobility matter most |
Children and teenagers are assessed with BMI-for-age percentile charts instead of the adult bands: a child between the 85th and 95th percentile for their age and sex is classed as overweight, and at or above the 95th percentile as obese. The adult calculator on this page must never be used for children.
Why BMI Alone Is Not Enough
BMI is one number, and one number cannot describe a body. It has real blind spots, and honest calculators say so. Use it as a first check, then add the checks that fix its gaps.
- It cannot tell muscle from fat. A rugby player weighing 100 kg at 1.80 m has a BMI of 30.9, technically obese — but if a body fat check shows 14%, the player is clearly not carrying excess fat.
- It ignores where fat sits. Abdominal fat, packed around the organs, drives far more health risk than fat on the hips and thighs, and two people with identical BMIs can carry very different waistlines.
- It does not adjust for age, sex, or ethnicity. Older adults, women, and people of South or East Asian descent all need the number read with different context — for many Asian populations, risks start rising at a BMI of 23 rather than 25.
- It says nothing about fitness. A person with a BMI of 28 who exercises regularly, eats well, does not smoke, and has normal blood pressure and blood sugar is at lower risk than a sedentary person with a BMI of 24 and poor metabolic markers.
The practical combination for most adults is BMI plus waist size, checked monthly, with a body fat percentage estimate added when the two disagree or when you train seriously. If your BMI says overweight but your waist is fine and you lift weights, body fat percentage is the tie-breaker. If your BMI is healthy but your waist is over the cut-off, the waist number deserves more attention than the BMI.
What to Do After Your Result
Your result points to a next step. Pick the one that matches your band and start there — small, boring plans kept for months beat dramatic overhauls every time.
- Healthy (18.5–24.9). Keep doing what works. Recheck monthly, stay active, and keep your waist under half your height.
- Overweight (25.0–29.9). Work out your daily calorie needs with the calorie calculator and eat 250 to 500 kcal below maintenance. Add a 30-minute daily walk and check again in a month.
- Obese (30.0 and over). The same steps apply, plus a conversation with your doctor, especially if you have high blood pressure, high blood sugar, or joint pain.
- Underweight (below 18.5). Add calorie-dense foods and strength training, and see a doctor if the low weight is unintentional.
- Recheck monthly, not daily. Daily readings mostly track water fluctuation and scale noise. Compare monthly averages for the real trend.
How Often Should You Check Your BMI?
Monthly is plenty for most adults. Weight moves by 1 to 2 kg day to day from water alone, so daily checks mostly measure noise and cause needless worry. Weigh weekly under identical conditions if you prefer — same time, same scale, same clothing — and compare monthly averages for the real trend. After a change in diet or activity, give it at least four weeks before judging the result, because the first weeks of any plan are mostly water and glycogen, not fat.
- Same time: morning, after the bathroom, before eating or drinking.
- Same scale: home scales disagree by a kilogram or more, so stick to one.
- Same conditions: light clothing, no shoes, hard floor, never carpet.
- Same record: write it down or log it, so the trend is visible instead of remembered.
Related tools on this site: the main BMI calculator for a quick check, the body fat calculator for fat versus lean mass, the ideal weight calculator for your target range, and the TDEE calculator for how many calories you actually burn each day.
Frequently Asked Questions
What is my BMI if I weigh 70 kg and I am 175 cm tall?
Your BMI is 22.9, which is in the healthy range. The calculation is 70 ÷ 1.75² = 70 ÷ 3.0625 = 22.9, and your BMI prime is 0.91. Your healthy weight range at that height is 56.7 to 76.3 kg.
What is a good BMI?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. That band is linked to the lowest risk of weight-related disease in large population studies, though individual health depends on much more than one number.
Is BMI accurate?
As a population screening tool, BMI is well validated. As an individual verdict, it is limited: it cannot tell muscle from fat, ignores where fat sits, and does not adjust for age, sex, or ethnicity. Pair it with waist size and body fat percentage for a fairer picture.
Does BMI differ for men and women?
The formula is identical, but women naturally carry a higher body fat percentage at the same BMI. The categories are the same for both sexes; interpretation should account for body composition.
Can I use this BMI calculator for my child?
No — children and teenagers need age- and sex-specific BMI percentile charts, not the adult cut-offs. Ask your paediatrician for the right assessment.
How often should I check my BMI?
Monthly is plenty for most adults. Daily checks mostly track water fluctuation and scale noise. Weigh weekly under identical conditions if you prefer, and compare monthly averages for the real trend.
Disclaimer: This calculator is for general information only and is not medical advice. BMI is a screening measure, not a diagnosis. Talk to a healthcare professional about your weight and health.