BMI Calculator
⚡ Runs locally🔒 No uploads🆓 Free, no sign-up
BMI (Body Mass Index) is your weight in kilograms divided by the square of your height in meters. Proposed by Adolphe Quetelet in the 19th century, it is the world's most widely used body-composition screening metric — not because it is perfect, but because it is cheap, reproducible and comparable across populations. It compresses the otherwise unanswerable question “what weight is right for my height?” into a single number: a 170 cm / 65 kg person and a 180 cm / 75 kg person get 22.5 and 23.1, directly comparable. The WHO uses it to classify population weight status, and insurers, clinics and the fitness industry all use it as the entry-level indicator.
Three everyday uses stand out. First, reading a checkup: once you have the number, the category tells you whether to maintain, lose or gain — and whether follow-up checks like body-fat percentage or waist circumference are worth doing. Second, anchoring a weight-loss plan: compute your current BMI, then the weight that corresponds to the top of the healthy range; the difference is a concrete number of kilograms to lose, which beats a vague “get slimmer.” Third, sanity-checking training progress: when the scale goes up during strength training, BMI plus a body-fat reading tells you whether you gained muscle or fat.
Know the limits before trusting the number. BMI cannot tell muscle from fat — a lifter with serious muscle mass can land in “overweight” without carrying excess fat. It does not apply directly to pregnant people (follow your doctor's guidance), children (use age-and-sex percentile curves), or some older adults (muscle loss can mask risk behind a “normal” BMI). Cutoffs also differ by ethnicity: at the same BMI, Asian populations tend to carry more body fat, so China commonly uses stricter lines (24–27.9 overweight, 28+ obese) than the WHO's 25/30. This page shows the WHO bands and notes the Chinese ones so you can read both.
Using this page is straightforward: enter height in centimeters and weight in kilograms and everything updates live — the big BMI number, the category, a color gauge marking your position (blue underweight, green healthy, yellow overweight, red obese), plus the healthy weight range for your exact height. Hit “Copy result” to send the number to a coach or doctor, or log it in your own health records. All math runs locally in your browser; nothing is uploaded or stored.
How to use
- Enter your height (cm) and weight (kg) above — the BMI updates live, no button needed.
- Read the large BMI number, the weight category (Underweight / Healthy / Overweight / Obesity) and your position on the color gauge.
- Check the “Healthy weight range” line to see what weight range fits your height.
- Use “Copy result” to share the number with a coach or doctor, or “Clear” to start over.
FAQ
How is BMI calculated?
Weight in kilograms divided by height in meters squared. Example: 170 cm and 65 kg → 65 ÷ 1.7² ≈ 22.5. Squaring height removes the natural effect of height on weight so people of different heights can be compared fairly.
What BMI is considered normal?
WHO bands: under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30+ obese. China commonly uses stricter cutoffs — 18.5–23.9 normal, 24–27.9 overweight, 28+ obese — because Asian populations tend to carry more body fat at the same BMI. Consider waist circumference alongside BMI.
I'm muscular and my BMI says overweight — is that wrong?
Probably a false alarm. BMI cannot distinguish muscle from fat, so trained lifters often score “overweight” while being lean. Combine it with body-fat percentage and waist measurements instead of judging by BMI alone.
Does it work for children, pregnancy or older adults?
Not directly. Children are assessed with age-and-sex percentile curves, pregnancy weight management should follow a doctor's guidance, and older adults can hide malnutrition or sarcopenia behind a “normal” BMI. Treat the number as a rough reference for these groups.
Is my height and weight uploaded anywhere?
No. Every calculation happens locally in your browser — your inputs never touch a server and are never recorded. Close the page and they're gone; the tool even works offline.