How to use the bmi calculator
- 1Choose metric or US units.
- 2Enter your height and weight.
- 3Read your BMI and where it sits on the scale.
- 4Check the healthy weight range for your height.
How BMI is calculated
Body mass index is weight in kilograms divided by height in meters squared:
BMI = weight (kg) ÷ height (m)²
For 68 kg and 1.70 m: 68 ÷ 2.89 = 23.5. In US units the calculator converts pounds and inches first.
Adult categories
These are the World Health Organization categories for adults:
- below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 and above: obesity
What BMI does not tell you
BMI is a quick screening measure, not a diagnosis. It does not distinguish muscle from fat, so very muscular people can score as overweight. It also does not show where fat is carried, and healthy ranges can differ by age and ethnicity. Children and teenagers are assessed with age- and sex-specific percentiles instead.
Talk to a doctor or nurse for advice about your own weight and health.
Frequently asked questions
What is a healthy BMI?
For most adults, 18.5 to 24.9. Some health services use lower thresholds for people of certain ethnic backgrounds.
Is BMI accurate for athletes?
Not always. Muscle weighs more than fat, so muscular people can have a high BMI without excess body fat.
Can children use this calculator?
No. Children and teens need BMI-for-age percentiles, which compare them with others of the same age and sex.
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