BMI Calculator

Body mass index is the quickest widely used screening number for weight status: weight in kilograms divided by height in metres squared. Doctors, insurers, and fitness programs use it as a first filter because it needs only two measurements — and this calculator gives you the number, its category, and its context the moment you type.

Enter your weight and height in metric or imperial units and the result appears live: your BMI to one decimal place, a colour-coded category badge, and a gauge showing where you sit on the scale from 15 to 40. An insight panel translates the number into something actionable — the healthy weight range for your specific height, and approximately how much you would need to gain or lose to reach it. A checkbox switches to the WHO's Asian and South-Asian public-health cutoffs, which flag increased risk from BMI 23 rather than 25, because metabolic risk rises at lower BMI values in those populations.

BMI's main limitation is worth stating plainly: it measures mass, not composition. A muscular athlete can register as overweight while carrying little fat, and the standard adult categories do not apply to children, teenagers, or during pregnancy. Treat the result as one general screening signal — the calculator says so in its own disclaimer — and pair it with the Body Fat Percentage Calculator for a composition-based estimate, or the Calorie Calculator to plan a change. Everything is computed in your browser and your measurements are not uploaded anywhere.

The calculation is the standard formula: BMI = weight (kg) ÷ height (m)², applied live to your inputs (imperial entries are converted to metric first). The result maps to the WHO adult categories — under 18.5 underweight, 18.5–25 normal, 25–30 overweight, 30+ obese — or, with the checkbox on, to the WHO 2004 Asian action points of 18.5–23 normal, 23–27.5 increased risk, and 27.5+ high risk.

The healthy-range figure inverts the formula for your height: the lower bound is 18.5 × height² and the upper bound 25 × height² (or 23 × height² with Asian cutoffs). The gain/lose estimate is simply the difference between your current weight and the nearer bound. All arithmetic happens in your browser on each keystroke.

BMI measures weight relative to height and nothing else: it cannot see body composition, so muscular people can be misclassified upward and people with low muscle mass downward. The adult categories do not apply to children, teenagers, or during pregnancy. The healthy-range and gain/lose figures are arithmetic consequences of the formula, not personalized recommendations. Standard and Asian cutoff sets are provided, but individual risk depends on far more than one index — the built-in disclaimer says it plainly: a screening tool, not a diagnosis.

The component runs fully client-side. Canonical state is metric (kg, cm); imperial inputs convert on entry using 2.2046 lb/kg and 2.54 cm/in. BMI is computed as kg ÷ m² and displayed to one decimal. Category lookup uses the WHO adult bands or the WHO 2004 Asian action points depending on the checkbox. The gauge maps BMI 15–40 onto a colour-banded bar. Validation requires positive weight and height (weight ≤ 500 kg, height ≤ 275 cm flagged as invalid).

Standard vs. Asian / South-Asian cutoffs

The lower action points reflect evidence that metabolic risk rises at lower BMI values in Asian and South-Asian populations.

Anyone wanting a quick, private read on their weight status; people who have had a BMI quoted at them by a doctor, insurer, or gym and want to understand it; and those planning a weight change who want a height-appropriate target. It is an adult screening tool — parents checking a child's weight status need paediatric percentile charts instead.