Home/Calculators/BMI calculator
CalculatorBMI Calculator
Body mass index from metric or imperial measurements, with the WHO weight category and a healthy weight range for your entered height. BMI is a population-level screening figure, not a diagnosis — the limitations section below explains what it does and doesn't measure.
BMI
—
Not medical advice. BMI is a screening tool, not a diagnosis. See the limitations section below, and speak to a qualified health professional about what your own figures mean.
The WHO categories
| Category | BMI range (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese | 30.0 and above |
The formula is weight in kilograms divided by height in metres squared: BMI = kg ÷ m². It was designed in the 19th century as a population-statistics tool, not a clinical instrument for judging one individual — a distinction that matters more than the arithmetic itself.
WHO's separate action points for Asian populations
Population studies found that cardiovascular and metabolic risk (type 2 diabetes, hypertension) rises at lower BMI values in many Asian populations than in the population the original bands were built from. WHO has published supplementary action points reflecting this:
| Risk level | Standard band | Asian action point |
|---|---|---|
| Increased risk (overweight-equivalent) | 25.0+ | 23.0+ |
| High risk (obese-equivalent) | 30.0+ | 27.5+ |
This tool reports the standard WHO category, since that's the globally published default, but if the lower Asian action points are more relevant to you, use them as the frame instead — a BMI of 24 is "normal" on the standard scale but already past the increased-risk action point on the Asian-population scale.
What BMI does not measure — the honest limits
- Muscle vs fat. BMI cannot distinguish lean mass from fat mass. A muscular athlete and a sedentary person of the same height and weight get the identical BMI, despite very different body composition and health risk.
- The height-squared assumption. Dividing by height squared is a population-level curve fit, not a law of biology built for any one person. It systematically runs a little high for very short people and a little low for very tall people, because body mass doesn't scale with height squared in reality — it scales somewhere between squared and cubed, and the exponent varies by build.
- No age, sex or fat-distribution data. Where fat is carried (waist vs hips) is independently linked to health risk and BMI says nothing about it. It also doesn't adjust for age-related muscle loss or for pregnancy.
- It is a screening signal, not a diagnosis. A BMI outside the "normal" band is a prompt to look further, using better tools (waist circumference, body composition scanning, a clinician's assessment) — not a verdict on its own.
Questions people ask
Is a BMI-based "healthy weight range" the same as my ideal weight?
No. It's the weight range that would place you inside the 18.5–24.9 standard band at your entered height — a wide statistical band, not a personal target. Two people at opposite ends of that range can be equally healthy.
Does BMI work the same way for children?
No. Children's BMI is interpreted using age- and sex-specific percentile charts, not the flat adult bands shown here. This calculator is built for adults only.
Why does the tool warn about muscle mass specifically?
Because it's the most common real-world case where BMI misleads: strength athletes and very muscular people are frequently flagged "overweight" or "obese" by BMI alone despite low body fat, simply because muscle is denser than fat and BMI can't see the difference.
Should I use the standard or the Asian action points?
That depends on which population's risk research is more representative of your own background, and it's a judgement worth discussing with a health professional rather than deciding from a website. This tool shows both tables so you have the numbers either way.