How to calculate BMI online (metric and US units)

You can calculate BMI with a formula or with an online calculator. The math is the same whether you use metric or US customary units.

Metric formula

BMI = weight (kg) / [height (m)]²

Example: 70 kg at 1.75 m → 70 / (1.75 × 1.75) ≈ 22.9 (Normal on the adult WHO scale).

US formula

BMI = 703 × weight (lb) / [height (in)]²

Example: 160 lb at 70 in (5′10″) → BMI ≈ 23.0.

Beyond the number

A detailed calculator can also show a healthy weight range for your height (BMI 18.5–25), BMI Prime (BMI ÷ 25), and Ponderal Index (weight ÷ height³). Those extras are still educational - not medical advice.

Use the free BMI calculator with metric or US inputs. Results stay in your browser.
Calculate BMI online free →