Enter your height and weight in metric or imperial and this tool returns your Body Mass Index and its category. BMI is a ratio of weight to height squared. It doesn't measure body fat directly, but across a large population it tracks health risk closely enough that clinicians use it as a fast first screen.
The BMI categories
For adults, the standard World Health Organization ranges are:
- Under 18.5 — Underweight
- 18.5 – 24.9 — Normal (healthy) weight
- 25 – 29.9 — Overweight
- 30 and above — Obese (Class I 30–34.9, Class II 35–39.9, Class III 40+)
The formula is weight (kg) ÷ height (m)². In imperial units it's weight (lb) ÷ height (in)² × 703. The same cutoffs apply to adult men and women.
Where BMI genuinely falls short
BMI is a screening number, not a diagnosis, and it's wrong for some people in predictable ways:
- Muscle reads as weight. A muscular athlete can land in the "overweight" or even "obese" band with low body fat, because muscle is dense.
- "Normal" can hide risk. Someone sedentary with little muscle may sit at a healthy BMI while carrying an unhealthy fat percentage — sometimes called "skinny fat."
- It ignores where fat sits. Fat around the abdomen is more strongly linked to metabolic disease than fat on the hips and thighs, and BMI can't see the difference.
- Population differences matter. The standard ranges are based mostly on adults of European descent. The WHO has proposed lower thresholds for people of Asian descent, who can face raised metabolic risk at a lower BMI (around 23 for overweight).
- It doesn't apply cleanly to children, pregnant people, or frail older adults, who use different charts.
Read your number in context
Treat BMI as one signal, not a verdict. If you lift weights, run, or are very lean, the category may mislabel you — pair it with body fat percentage or a tape measure. And no online number replaces a conversation with a doctor who can factor in your blood pressure, blood work, and family history.
A better 30-second check
Waist-to-height ratio: divide your waist measurement by your height in the same units, and aim to keep it under 0.5. It captures abdominal fat that BMI misses and often predicts metabolic risk better — for the cost of one tape measurement.
FAQ
What is a healthy BMI?
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For most adults, 18.5 to 24.9 is the normal range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. The cutoffs are the same for adult men and women.
Is BMI accurate for athletes and muscular people?
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Frequently not. BMI can't separate muscle from fat, so muscular people often score as overweight while carrying very little fat. If that's you, body fat percentage or a waist measurement is far more informative.
How is BMI calculated?
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Weight in kilograms divided by height in metres squared. In imperial, it's weight in pounds ÷ height in inches squared × 703. This tool handles either unit system for you.
Do the categories apply to everyone equally?
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No. The standard ranges come mainly from European-descent populations. The WHO suggests lower thresholds for people of Asian descent, and BMI is interpreted differently for children, pregnancy, and older adults.
Is my data private?
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Yes. Everything is calculated locally in your browser. Your height and weight are never uploaded, logged, or shared.