BMI Calculator

Body mass index in metric or imperial units, with the healthy-weight range for your height — and an honest account of what BMI cannot tell you.

Editorially Reviewed Updated June 15, 2026

Enter your height and weight

Nothing you type is sent anywhere. The result updates as you type.

Height — feet

Height — inches

Weight — pounds

Enter your height and weight to see your BMI.

What this tool can and cannot tell you

BMI is a ratio of weight to height. It does not measure body fat, muscle, bone, or where fat is stored, so a muscular athlete and a sedentary adult can share a BMI and have very different health risk.
The 18.5–24.9 healthy range was derived largely from white European and North American populations. For adults of South Asian, Chinese, Japanese, Korean and some other Asian backgrounds, higher risk is often recognised from about 23.
It is not designed for children and teenagers (who need age-and-sex percentile charts), for pregnancy, or for people with significant fluid retention.
It says nothing about blood pressure, cholesterol, blood sugar, fitness or diet — the things that actually drive risk. A normal BMI is not a clean bill of health.
Waist circumference adds information BMI cannot: for most adults, a waist over 40 inches (102 cm) for men or 35 inches (88 cm) for women signals more metabolic risk at any BMI.

What BMI actually measures

Where the number comes from, why it survives despite its flaws, and what to measure alongside it.

Body mass index is your weight in kilograms divided by the square of your height in metres. It was devised in the 1830s by the Belgian statistician Adolphe Quetelet as a way of describing populations, not individuals — and that origin explains both its usefulness and its limits. Across a large group, average BMI tracks reasonably well with average body fatness and with rates of conditions like type 2 diabetes and cardiovascular disease. Applied to one person, it is a crude proxy that can be badly wrong in either direction.

How to measure yourself properly

Weigh yourself in the morning, after using the bathroom and before eating or drinking, wearing little or nothing, on the same scale each time. Body weight swings by one to two kilograms (two to four pounds) across a day from food, fluid and salt, so a single reading is noisy; the weekly average is the signal. For height, stand without shoes, heels together, back against a wall, looking straight ahead — most adults have lost a little height since the number on their driving licence was recorded, and using an old figure quietly inflates BMI.

What changes it

BMI moves when weight moves, and weight responds to energy balance over weeks and months rather than days. Strength training can raise it while body composition improves, which is one of the clearest illustrations of why the number alone is not the goal. Some medicines — corticosteroids, several antipsychotics and antidepressants, insulin, some seizure medicines — cause weight gain that has nothing to do with effort. Thyroid disease, fluid retention from heart or kidney conditions, and pregnancy all move weight for reasons a BMI band cannot interpret.

What to look at alongside it

Waist circumference tells you about abdominal fat, which is the deposit most closely tied to metabolic risk. Blood pressure, fasting glucose or HbA1c, and a lipid panel tell you what is happening inside. Fitness matters independently: people who are active carry lower risk at every BMI. If your BMI sits outside the healthy band, the productive next step is a conversation about those measures, not a target weight pulled from a chart.

Frequently asked questions

Is BMI accurate for athletes?

Often not. Muscle is denser than fat, so people who train seriously for strength frequently land in the "overweight" or even "obese" band while carrying little fat. If you lift regularly and your waist is unremarkable, BMI is probably telling you about your muscle, not your risk.

Why do some guidelines use a lower cut-off for people of Asian descent?

Population studies found that adults of South Asian, Chinese, Japanese and Korean ancestry tend to develop type 2 diabetes and cardiovascular disease at lower BMIs than white European populations, partly because of where fat is stored. The World Health Organization and several national bodies therefore recognise raised risk from around a BMI of 23 in these groups.

Can I use this calculator for my child?

No. Children and teenagers are assessed against age-and-sex-specific percentile charts, because healthy body composition changes throughout growth. Ask your paediatrician or practice nurse, who will plot the reading on a growth chart.

My BMI is in the healthy range. Does that mean I am healthy?

It means one screening measure looks unremarkable. Blood pressure, blood sugar, cholesterol, smoking, activity, sleep and family history all sit outside what BMI can see, and it is entirely possible to have a normal BMI alongside any of them.

Sources

Centers for Disease Control and Prevention — Adult BMI — BMI categories and their intended use as a screening measure
National Heart, Lung, and Blood Institute — Overweight and Obesity — Waist circumference thresholds and combined risk assessment
World Health Organization — Obesity and Overweight — International classification and the lower cut-offs used for some Asian populations

Health Captain links to primary public-health and clinical sources so you can read the original material yourself. See our sources policy.

About this calculatorThis BMI calculator is an educational screening tool. It does not diagnose obesity or any other condition, it cannot assess your individual health risk, and it is not appropriate for children, pregnancy, or people with significant fluid retention. Discuss weight and body composition with a clinician who knows your history.

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