BMI Calculator
Work out Body Mass Index from height and weight, in metric or imperial, with the standard adult category.
Results are provided as is, for general information. Check anything important before relying on it. See the Terms of Use.
About this tool
Body Mass Index divides weight by the square of height — kilograms over metres squared in metric, or pounds over inches squared scaled by a fixed 703 conversion factor in imperial, so both unit systems land on the same score. The result is checked against the standard WHO/CDC adult bands: under 18.5 is underweight, 18.5 up to 25 is normal weight, 25 up to 30 is overweight, and 30 and over is obese. It is a population-level screening number, not a diagnosis — a heavily muscled athlete and a sedentary adult can share a BMI while having very different body compositions, and the adult bands don't apply to children, teenagers or pregnant people. Runs entirely in your browser.
How it works
Metric: BMI = weight (kg) ÷ height (m)² Imperial: BMI = 703 × weight (lb) ÷ height (in)²
The adult categories are: under 18.5 underweight, 18.5 to 24.9 normal weight, 25 to 29.9 overweight, and 30 or more obese. BMI does not distinguish muscle from fat and uses different charts for children.
| Question | Working | Answer |
|---|---|---|
| BMI for 175 cm and 70 kg | 70 ÷ 1.75² | 22.9 (normal weight) |
| BMI for 5 ft 9 in (69 in) and 180 lb | 703 × 180 ÷ 69² | 26.6 (overweight) |
When to use it
Questions
Is BMI accurate for everyone?
No — it's a population screening tool, not an individual diagnosis. It can't tell muscle from fat, so athletes and very muscular people are routinely flagged 'overweight' or 'obese' despite low body fat, and it doesn't account for bone density, age-related muscle loss, or where fat is distributed on the body. It's most useful as a rough starting point, not a final word.
Why does the imperial formula use 703?
It's the metric formula rewritten in pounds and inches. Converting weight from pounds to kilograms (×0.453592) and height from inches to metres (×0.0254, squared) and folding those constants together gives weight × 703.07 / height², rounded to 703. Same calculation, different starting units.
Do the same bands apply to children or during pregnancy?
No. The underweight/normal/overweight/obese cutoffs here are the adult bands. Children and teenagers are assessed against age- and sex-specific percentile charts instead, since a healthy BMI changes as kids grow, and pregnancy weight gain isn't screened with adult BMI bands either.
What counts as a 'healthy' BMI number?
18.5 to 24.9 is the broad normal-weight range used by most health organizations, but it's a wide band — a doctor looking at an individual would also weigh waist circumference, activity level, family history and other markers, not BMI alone.
Does it store or send my height and weight anywhere?
No. Like the site's other calculators, this one runs entirely in your browser — nothing you type is uploaded, logged or sent to a server.