How the BMI calculator works
Body mass index is a quick screening number that relates weight to height. The calculator converts your measurements to kilograms and meters, divides weight by height squared, and places the result in the standard adult categories used by the CDC and World Health Organization. It also shows the weight range that corresponds to a BMI of 18.5 to 24.9 for your height.
The formula
BMI = weight (kg) ÷ height (m)2. In U.S. units, BMI ≈ 703 × weight (lb) ÷ height (in)2.
Adult BMI categories
- Under 18.5 — underweight
- 18.5 to 24.9 — healthy weight
- 25 to 29.9 — overweight
- 30 and above — obesity
Example
A person who is 5 feet 9 inches (69 inches) tall and weighs 160 pounds has a BMI of 703 × 160 ÷ 69², or about 23.6, which falls in the healthy range. In metric, 70 kg at 175 cm gives a BMI of 22.9.
What BMI does not tell you
BMI does not measure body fat directly. Muscular people can have a high BMI while being very fit, and older adults may have a normal BMI with low muscle mass. It also ignores where fat is stored; waist size is another useful measure. These adult categories do not apply to children and teens, who are assessed with age- and sex-specific percentiles. Treat BMI as a starting point for a conversation with your doctor, not a diagnosis.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI from 18.5 to 24.9 is considered a healthy weight range.
Is BMI accurate for athletes?
Not always. Muscle is dense, so athletes can have a high BMI without excess body fat.
Can children use this calculator?
No. Children and teens use BMI-for-age percentiles that depend on age and sex.
Is BMI different for men and women?
The adult formula and categories are the same for both, although body composition differs.
Results are estimates for educational purposes only and are not financial, tax, legal or medical advice. See our disclaimer. Last reviewed 2026-10-22.