Invented for statistics
BMI was created in the 1830s by Lambert Adolphe Quetelet to study population trends—not to size up individual health.
Origins
Body Mass Index (BMI) Calculator
Inputs
For adults (20+). Ages 2–19 require growth-chart interpretation with a professional.
Result
Your BMI
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Category
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Health Risk
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Formula
Metric: BMI = weight(kg) / [height(m)]²
Imperial: BMI = weight(lbs) / [height(in)]² × 703
Examples
Adult BMI categories
| Category | BMI |
|---|---|
| Underweight | < 18.5 |
| Normal (Healthy weight) | 18.5–24.9 |
| Overweight | 25.0–29.9 |
| Obese | ≥ 30 |
What is BMI and how is it calculated?
Body Mass Index (BMI) is a simple ratio of weight to height. In metric units:
BMI = weight(kg) / [height(m)]². In imperial units:
BMI = weight(lbs) / [height(in)]² × 703. This tool supports both systems and calculates instantly in your browser.
Adult BMI categories
- Underweight: < 18.5
- Normal (Healthy weight): 18.5–24.9
- Overweight: 25.0–29.9
- Obese: ≥ 30
Important caveats
- Not body fat: BMI doesn’t distinguish fat from muscle.
- Athletes & muscular builds: Can read “high” without excess fat.
- Age, sex, ethnicity: Health risks at a given BMI can differ.
- Children/teens (2–19): Use growth-chart–based interpretation with a professional.
Disclaimer: This BMI calculator is for general information and adult screening only and is not medical advice.
5 Fun Facts about BMI
Why “×703”?
The imperial formula multiplies by 703 (technically 703.0696) to convert inches/pounds into the metric-based equation.
Unit quirk
Space stretch
Astronauts can “grow” up to 2 inches in microgravity. Same weight, taller height—so their BMI would dip on orbit.
Zero-G twist
Same BMI, different body fat
Two people with the same BMI can have very different body fat levels; women often carry 7–10% more body fat than men at the same BMI.
Hidden differences
Global cutoffs vary
Some Asian guidelines flag “overweight” starting near BMI 23 (not 25) because risks rise at lower values in those populations.
Regional view