BMI Calculator
Calculate your Body Mass Index to assess whether your weight is healthy.
Precision Fitness Calculators
Calculate your Body Mass Index to assess whether your weight is healthy.
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Scientific Reference
Body Mass Index (BMI) was developed by Belgian mathematician Adolphe Quetelet in the 1830s. It provides a simple numeric measure of a person's thickness or thinness.
The Formula
- BMI = weight (kg) ÷ height² (m²)
WHO Classification
- Underweight: BMI < 18.5
- Normal weight: BMI 18.5 – 24.9
- Overweight: BMI 25.0 – 29.9
- Obese Class I: BMI 30.0 – 34.9
- Obese Class II: BMI 35.0 – 39.9
- Obese Class III: BMI ≥ 40.0
What BMI tells you — and what it does not
Body Mass Index divides your weight in kilograms by your height in metres squared. It is the screening tool used by the WHO and most health systems because it needs only a scale and a tape measure, and at the population level it tracks disease risk well: risk of type 2 diabetes, hypertension and cardiovascular disease climbs as BMI moves above the normal range.
BMI cannot see body composition. A muscular lifter can read "overweight" while carrying less fat than a sedentary person with a "normal" BMI — the skinny-fat pattern common among desk workers. Use BMI as a first screen, then confirm with the Body Fat calculator (US Navy method) or a waist measurement, which capture where the weight actually is.
Why South Asians need lower cutoffs
The standard WHO thresholds (overweight at 25, obese at 30) were derived largely from European populations. South Asians develop visceral fat, insulin resistance and type 2 diabetes at markedly lower BMIs — the "thin outside, fat inside" phenotype. The WHO expert consultation therefore recommends action points of 23 (increased risk) and 27.5 (high risk) for Asian populations.
Practically: if your heritage is South Asian and your BMI is 23–24.9, do not read "normal" as "nothing to do". That range is exactly where lifestyle change pays off most — a modest calorie deficit, resistance training to add muscle, and a daily step target. This calculator shows the standard WHO classes; keep the Asian action points in mind when interpreting yours.
A useful companion check costs nothing: measure your waist and divide it by your height. Staying under 0.5 — waist less than half your height — is a simple rule that flags abdominal fat regardless of ethnicity or build, and it catches exactly the cases where BMI misleads. Someone with a BMI of 24 and a waist-to-height ratio of 0.56 has a problem the BMI reading hides. Track both monthly, measured at the same time of day, and treat a falling waist measurement as a better sign of progress than a falling scale weight, because it means you are losing the fat that actually drives metabolic risk rather than the muscle that protects against it.
Frequently Asked Questions
What is a healthy BMI?
The WHO defines the normal range as 18.5–24.9. For South Asian and other Asian populations, the WHO recommends lower action points: increased risk starts at 23 and high risk at 27.5, because metabolic disease appears at lower BMIs in these groups.
Can BMI be wrong for muscular people?
Yes. BMI cannot distinguish muscle from fat, so heavily muscled people can be classed overweight or obese while lean. If you strength train seriously, judge progress by body fat percentage and waist measurement instead.
Is BMI or body fat percentage better?
Body fat percentage is the more informative number because it measures composition, not just mass. BMI wins on convenience. Best practice is to use both: BMI as a quick screen, body fat and waist-to-hip ratio to confirm what the weight is made of.
What should I do if my BMI is in the overweight range?
Start with a modest calorie deficit of 15–20% below your TDEE, add 2–3 resistance sessions a week to protect muscle, and re-measure monthly. A sustainable 0.5 kg per week of loss outperforms any crash diet over a year.