ToolBMI Calculator
Your body mass index in metric or imperial — with the honest fine print.
What BMI is — and isn't
Body Mass Index is a quick screening ratio between weight and height, useful because it needs no equipment and correlates with health risk across large populations. It is not a body-fat measurement: it can't tell a rugby player from a couch potato of the same height and weight, it shifts meaning with age and ethnicity, and it says nothing about where weight sits (belly fat carries more risk than the same weight elsewhere). Treat an out-of-range BMI as a prompt to look closer — ideally with a professional — not as a verdict.
WHO adult categories
- Below 18.5 — underweight
- 18.5 – 24.9 — healthy range
- 25.0 – 29.9 — overweight
- 30.0+ — obese
This tool is for general information, not medical advice. Nothing you enter leaves your browser.
Frequently Asked Questions
How is BMI calculated?
BMI = weight (kg) divided by height (m) squared. In imperial units it is weight (lb) × 703 ÷ height (in)². A 70 kg person at 1.75 m has a BMI of 70 ÷ 3.0625 ≈ 22.9.
What is a healthy BMI range?
For most adults, the WHO ranges are: under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, and 30+ obese. These are population-level screening bands, not individual diagnoses.
Is BMI accurate for athletes?
Often not. BMI cannot tell muscle from fat, so muscular people frequently score "overweight" while carrying little fat. Waist circumference and body-fat percentage are better follow-up measures if your BMI looks off for your build.
Does BMI apply to children?
Not with adult ranges. Children and teens use age- and sex-specific percentile charts. This calculator is designed for adults 20 and over.