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Health · BMI

BMI Calculator

Estimate body mass index from height and weight.

BMI Calculator

Choose your sex, enter your age, choose a unit system, enter your height and weight, then select Calculate.

How this is calculated

Body mass index compares weight to height: Metric: BMI = weight(kg) ⁄ height(m)² US: BMI = 703 × weight(lb) ⁄ height(in)² The result falls into one of four standard adult categories: underweight, normal, overweight, or obese. A visual gauge below the result shows where your BMI falls among the four categories. Age and sex don't change this number for anyone — see "About this calculation" for why they're asked.

Examples

A person 5'10" (70 inches) tall weighing 160 lb has a BMI of about 23 — in the "Normal" range. The same BMI applies to someone 175 cm tall weighing about 70.4 kg.

About this calculation

BMI category thresholds (below 18.5 underweight, 18.5–25 normal, 25–30 overweight, 30 and above obese) are the standard adult ranges used by the WHO and CDC, and apply the same way regardless of age or sex. Those fixed ranges aren't the clinically appropriate interpretation for ages under 20 — the CDC instead defines pediatric BMI using age- and sex-specific percentile growth charts, which this calculator doesn't attempt to reproduce; a note appears below the result for that age range instead. BMI is a general screening tool, not a diagnosis — it doesn't account for muscle mass, bone density, or body composition.

Related tools

More calculators are on the way — browse everything planned on the Home page.

Frequently asked questions

Is BMI accurate for everyone?

BMI is a general screening tool based only on height and weight — it doesn't distinguish muscle from fat, so it can be misleading for very muscular people, older adults, or children. It's a starting point, not a full health assessment.

Why does the calculator ask for age and sex if they don't change the BMI number?

BMI itself depends only on height and weight. Age is used only to show the right caveat for ages under 20, where the fixed adult categories don't apply — the underlying BMI number is the same for everyone at a given height and weight, at any age.

Why does the calculator say my input is invalid?

Height and weight must both be positive numbers, and age must be a whole number between 2 and 120 — check that you've filled in every visible field for your chosen unit system.