Enter your height and weight in either metric or US customary units to calculate your Body Mass Index and see the WHO weight category it falls into.
How to Use the BMI Calculator
Flip the unit toggle to Metric or US first, then fill in height and weight — switching units re-derives the figures rather than just relabeling them, and the WHO category updates alongside the number.
Two numbers, one ratio: BMI squeezes height and weight into a figure doctors have used for population screening since the 1970s. It's not a diagnosis and never was — it's a fast, cheap proxy that works well across large groups and less well for any one individual standing in front of you.
The Formula
BMI = kg ÷ m²In pounds and inches, the same relationship becomes:
BMI = (lb ÷ in²) × 703The 703 isn't arbitrary — it's just the unit-conversion factor that makes the imperial version land on the same scale as the metric one.
The World Health Organization's four adult bands, which this tool uses directly: under 18.5 is underweight, 18.5–24.9 is normal weight, 25.0–29.9 is overweight, and 30.0 and up is obese. None of that is adjusted for age, sex, or ethnicity — it's the same four cutoffs for everyone in the "adult" bucket.
Where BMI Falls Apart
It can't tell muscle from fat, full stop. Weigh 200 pounds at 6 feet tall and BMI treats a bodybuilder and someone who's never lifted anything heavier than groceries identically, because the formula only ever sees the two numbers you typed in. That's the whole tool. Athletes, pregnant women, older adults, and anyone under 20 tend to get less useful numbers out of the standard bands for the same reason — body composition varies in ways height and weight alone can't capture. Waist-to-height ratio or an actual body-fat measurement gets closer to what people usually mean when they ask "am I a healthy weight," and kids need an age-specific percentile chart, not these adult cutoffs.
A result outside "normal" isn't a verdict. It's a reason to look further — with a real person, not a formula.
This tool is for general information, not medical advice. Talk to a doctor or registered dietitian about what your BMI, or any other body-composition figure, means for you specifically.