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
—
Category
—
Health Risk
—
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 quick way to relate weight to height and estimate weight status for adults. It is not a direct measure of body fat, but it is widely used by health professionals as a screening tool. This calculator helps you find your BMI and see which general category it falls into, so you can better understand your results at a glance.
The concept is simple: your weight is divided by the square of your height. In metric units, the formula is BMI = weight(kg) / [height(m)]². In imperial units, the formula is BMI = weight(lbs) / [height(in)]² × 703. The tool supports both systems and performs the calculation instantly in your browser.
How to use the BMI calculator:
- Select your unit system (metric or imperial).
- Enter your height and weight. You can also add age if you want it shown with your results.
- Click Calculate to see your BMI value and category.
- Use the table above to interpret where your result sits.
People use a BMI calculator for many practical reasons: tracking changes over time, setting general wellness goals, or preparing for a doctor visit. It can also be useful when comparing health metrics alongside other measurements such as waist circumference or body fat percentage. If you are starting a fitness plan, checking your BMI can provide a baseline to measure progress.
Important caveats: BMI does not distinguish between fat and muscle, so athletes and people with muscular builds can see a higher BMI without excess body fat. Health risks at a given BMI can also vary by age, sex, and ethnicity. For children and teens (ages 2–19), BMI should be interpreted using age- and sex-specific growth charts with a healthcare 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