How to Calculate BMI: A Complete Guide
By Calculator Atlas editorial (draft)Publication date pending5 min read
A simple guide to understanding Body Mass Index, its formula, and its limits.
What is BMI?
Body Mass Index (BMI) is a simple ratio of weight to height. It is widely used as a screening measure for weight categories, but it is not a diagnosis of health or body fat.
BMI formula
In metric units, BMI equals weight in kilograms divided by height in meters squared.
- BMI = weight (kg) ÷ height (m)²
- BMI = 703 × weight (lb) ÷ height (in)²
BMI chart
Adult BMI values are commonly grouped into the following categories.
| Category | BMI range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity | 30.0 and above |
How to calculate BMI
Convert your height to meters, square it, then divide your weight in kilograms by that number. A calculator removes the manual steps once the BMI tool is published.
Limitations of BMI
BMI does not distinguish muscle from fat, and it does not account for age, sex or body shape. Use it as one input among several, and speak to a health professional about your own situation.
Sources
World Health Organization. Body mass index classification for adults (below 18.5, 18.5 to 24.9, 25.0 to 29.9, 30.0 and above). Book-level citation; not checked against a specific page.
US Centers for Disease Control and Prevention. About Adult BMI: the BMI formula in metric and US units and its limits as a screening measure. Book-level citation; not checked against a specific page.