BMI Calculator

Formula

BMI = weight(kg) ÷ height(m)². US units: BMI = 703 × pounds ÷ inches². Prime = BMI ÷ 25.

Healthy band: 18.5×H² to 24.9×H². Ponderal Index = kg ÷ m³.

How it works

Enter height, weight, age and sex. The engine converts to metric, divides weight by height squared, then looks up the WHO adult band from severe thinness below 16 through normal 18.5–25 to obesity class III at 40+. It also reports BMI prime (distance to the 25 ceiling), the Ponderal cross-check that scales better at height extremes, and the healthy weight band for your exact height.

Assumptions

• Adult cutoffs (20+); ages 2–20 need CDC percentiles, not these bands.
• Average build; muscle, pregnancy, and edema distort the number.
• Barefoot standing height and morning weight; 1-inch error moves BMI ~0.5–1.

Default result

With Defaults: 5 ft 10 in, 160 lbs, age 25, male (US units): BMI 23.0 (Normal Weight) · healthy 58.6–78.9 kg at 178 cm

Worked examples

Healthy adult (metric)

178 cm, 72 kg, age 25, male

BMI = 72 ÷ 1.78² = 22.7 (Normal Weight) · healthy 58.6–78.9 kg — Example calculated with this calculator's formula.

Overweight adult (US)

5 ft 4 in (64 in), 165 lbs, age 40, female

BMI = 703×165 ÷ 64² = 28.3 (Overweight) — Example calculated with this calculator's formula.

Frequently asked questions

What is BMI and how is it calculated?

BMI (Body Mass Index) is your weight in kilograms divided by your height in meters squared: BMI = kg/m². In US units, BMI = 703 × pounds ÷ inches². It is a screening tool that categorizes weight status but does not measure body fat directly.

What is a healthy BMI range?

The WHO healthy range for adults is 18.5–24.9 kg/m². Below 18.5 is underweight (split into mild, moderate, and severe thinness), 25–29.9 is overweight, and 30+ is obese — further divided into Class I (30–34.9), II (35–39.9), and III (40+).

Is BMI accurate for athletes?

Frequently not. BMI cannot distinguish muscle from fat, so muscular athletes are often misclassified as overweight or obese despite low body fat. A 220 lb bodybuilder at 10% fat can register a BMI near 30. Use body fat percentage or waist-to-height ratio for athletic populations.

How does BMI differ for men and women?

The adult categories are identical for both sexes, but at the same BMI women typically carry about 10% more body fat than men. Pregnancy and menopause also shift composition in ways BMI does not capture.