Body Mass Index (BMI) is a quick, widely used way to screen for healthy body weight. Here's how it works — and its limitations.
The BMI formula
BMI = weight (kg) / height (m)²
To calculate it yourself: divide your weight in kilograms by your height in metres squared. Prefer pounds and inches? Multiply weight (lb) by 703 and divide by height (in) squared.
Our BMI Calculator does the math instantly.
What the categories mean
The World Health Organization classifies adult BMI as follows:
- Underweight — below 18.5
- Normal — 18.5 to 24.9
- Overweight — 25 to 29.9
- Obese — 30 and above
A BMI in the normal range is associated with lower risk of many chronic conditions, but it's only one part of the picture.
Important caveats
- BMI does not measure body fat directly.
- Very muscular people (including athletes) can have a high BMI with low body fat.
- Older adults and different ethnic groups may see different health risks at the same BMI.
Treat BMI as a screening starting point, not a diagnosis. For a fuller picture, combine it with waist circumference, body-fat estimates, and, ideally, professional guidance.
Track your weight goals alongside BMI with our Calorie Calculator and Ideal Weight Calculator.