BMI calculator
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- BMI = weight (kg) ÷ height (m)² = 70 ÷ 1.75² = 22.9.
- Adult ranges: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, 30 and over obesity (classes 1 to 3 from 30, 35 and 40).
- BMI is a screening number: it does not measure body fat and is not a diagnosis. It does not apply to children, who are assessed on growth charts.
| Inputs | Answer |
|---|---|
| Units: Metric (cm, kg); Height: 175; Weight: 70 | A BMI of 22.9 falls in the "Healthy weight" range for adults. |
| Units: US (inches, pounds); Height: 69; Weight: 154 | A BMI of 22.7 falls in the "Healthy weight" range for adults. |
| Units: Metric (cm, kg); Height: 160; Weight: 82 | A BMI of 32 falls in the "Obesity class 1" range for adults. |
How to use it
Body mass index is weight in kilograms divided by height in metres squared. For adults the World Health Organization and the CDC use these ranges: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, and 30 or more obesity (class 1 from 30, class 2 from 35, class 3 from 40).
BMI is a screening number: it does not measure body fat or where fat sits, and it can mislead for very muscular people, older adults and some ethnic groups. It does not apply to children, whose BMI is read against growth charts for their age. This is general information and an estimate, not medical advice; talk to a healthcare professional about your own situation.
Frequently asked questions
How is BMI calculated?
Weight in kg divided by height in metres squared. In US units: 703 × weight in pounds ÷ height in inches squared.
What is a healthy BMI?
For adults, 18.5 to 24.9 is the range labelled healthy weight by the WHO and CDC.
Is BMI accurate?
It is a quick screening tool, not a diagnosis; waist size and body composition give more information.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
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General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.