Free Online BMI Calculator
Check your body mass index in metric or imperial units and see your healthy weight range.
BMI is a screening tool, not a diagnosis. Muscle mass, age, and body composition can affect how it should be interpreted.
About the BMI Calculator
Body Mass Index (BMI) is a simple ratio of weight to height. It is widely used as a quick screening tool to place adults into weight categories: underweight, normal weight, overweight, and obese. This calculator supports both metric and imperial units.
The BMI formula
In metric units, BMI = weight (kg) ÷ height (m)2. In imperial units, the same result is obtained by multiplying weight in pounds by 703 and dividing by height in inches squared.
Adult BMI categories
- Below 18.5: underweight
- 18.5 – 24.9: normal weight
- 25.0 – 29.9: overweight
- 30.0 and above: obese
Limitations of BMI
BMI does not distinguish between muscle, fat, and bone. A muscular athlete may have a high BMI while carrying little body fat, and an older adult may have a normal BMI with low muscle mass. BMI is also interpreted differently for children, pregnant people, and some ethnic groups. Use it as a starting point, not a final answer.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. The healthy weight range shown is based on that range for your height.
Should I use metric or imperial?
Either works. Choose the units you normally use; the calculator converts them internally.
Is BMI accurate for athletes?
Not always. Muscle is denser than fat, so athletes can have a high BMI without excess body fat. Body composition measurements give a better picture.