How to use the BMI Calculator
- Choose metric (kg, cm) or imperial (lb, ft/in) units.
- Enter your height and weight.
- Read your BMI, its category and your healthy weight range.
What is BMI?
Body Mass Index (BMI) is a simple screening measure that relates your weight to your height. It is widely used by doctors and health organisations as a quick indicator of whether a person may be underweight, a healthy weight, overweight or obese.
BMI formula
BMI = weight (kg) ÷ height (m)²
In imperial units: BMI = 703 × weight (lb) ÷ height (in)².
BMI categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 and above | Obese |
BMI does not distinguish muscle from fat, so athletes may show a high BMI while being healthy. It is a screening tool, not a diagnosis — talk to a healthcare professional about your health.
Frequently asked questions
Is BMI accurate for everyone?
BMI is a useful population-level indicator but it does not account for muscle mass, bone density, age or ethnicity. Very muscular people can have a high BMI without excess fat.
Can children use this BMI calculator?
No. Children and teenagers are assessed using age- and sex-specific BMI percentiles. This calculator is for adults aged 20 and over.
What is a healthy BMI?
For most adults a BMI between 18.5 and 24.9 is considered a healthy weight range.