Free BMI Calculator
Free BMI calculator. Enter your height and weight in metric or imperial units to get your Body Mass Index and see which BMI category you fall into.
Our free BMI calculator works out your Body Mass Index from your height and weight, tells you which BMI category you fall into, and shows where you sit on the BMI scale — in both metric and imperial units.
What is BMI?
Body Mass Index (BMI) is a number calculated from a person's weight and height. It is widely used as a screening tool to identify whether a person is underweight, normal weight, overweight, or obese. BMI is defined as weight in kilograms divided by height in metres squared (kg/m²).
BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
How to calculate BMI
Metric: BMI = weight (kg) ÷ height (m)². For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.
Imperial: BMI = (weight (lbs) × 703) ÷ height (in)². For example, 154 lbs at 5 ft 9 in (69 in): (154 × 703) ÷ (69 × 69) = 22.7.
Limitations of BMI
BMI is a useful population-level screening tool, but it has limitations for individuals. It does not account for muscle mass, bone density, age, sex, or fat distribution. Athletes may have a high BMI due to muscle rather than fat. BMI should be used alongside other health indicators, not as a definitive measure of health. Always consult a healthcare professional for medical advice.