About the BMI Calculator
Body mass index compares weight against height to give a single screening number used by clinicians and health services worldwide. It is quick and useful at population level, but it says nothing about body composition — which is why the result here comes with the category boundaries and their limits clearly stated.
How to use the BMI Calculator
- Choose metric (cm and kg) or imperial (feet, inches and pounds).
- Enter your height and weight.
- Read your BMI value and the category it falls into.
- Check the healthy weight range shown for your height.
The formula behind it
Metric: BMI = weight in kg ÷ (height in metres)². Imperial: BMI = 703 × weight in pounds ÷ (height in inches)².
Frequently asked questions
What are the standard BMI categories?
Below 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight, and 30 or above falls in the obesity range. These are the World Health Organization thresholds for adults.
Why is BMI unreliable for athletes?
Muscle is denser than fat, so a heavily built athlete can post a BMI above 30 with very low body fat. BMI measures mass, not what that mass is made of.
Does BMI apply to children?
Not with these thresholds. Children and teenagers are assessed against age and sex-specific percentile charts, because healthy body composition changes throughout growth.
Should the thresholds differ by ethnicity?
Several health bodies use lower thresholds for people of South Asian, Chinese, and some other backgrounds, where cardiometabolic risk rises at a lower BMI. Ask a clinician what applies to you.
BMI is a general screening measure, not a diagnosis, and does not account for muscle mass, bone density, or fat distribution. Speak to a qualified health professional about your individual health.