What BMI tells you
Body mass index compares your weight with your height: weight in kilograms divided by height in meters squared. In US units, it is 703 × pounds ÷ inches². Doctors and public-health agencies such as the CDC and the World Health Organization use it as a quick screen for weight categories linked to health risks.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 to 34.9 | Obesity class 1 |
| 35 to 39.9 | Obesity class 2 |
| 40 and above | Obesity class 3 |
Worked example
A person who is 5 ft 9 in (69 inches) and weighs 160 lb has a BMI of 703 × 160 ÷ 69² = 23.6, in the healthy range. At that height, a BMI between 18.5 and 24.9 corresponds to about 125–169 lb.
Limits of BMI
BMI cannot tell muscle from fat, so athletes may score as overweight while being lean. It also says nothing about where fat is stored; waist size and body-fat percentage add useful information. For children and teens, BMI is interpreted with growth charts by age and sex.
How this works
The page converts your height to meters and your weight to kilograms (exactly, if you use inches and pounds), then divides the weight by the square of the height. The category uses the World Health Organization's adult cut-offs, the same as the CDC. The healthy range is the weight that gives a BMI of 18.5 to 24.9 at your height. BMI Prime is your BMI divided by 25, the upper limit of the healthy range.
Frequently asked
What is a healthy BMI?
18.5 to 24.9 for adults, according to the WHO and the CDC.
How is BMI calculated in pounds?
BMI = 703 × weight in pounds ÷ (height in inches)². For 160 lb and 69 in, that is 23.6.
Is BMI accurate for athletes?
Not always. Muscle is dense, so very muscular people can have a high BMI without excess fat.
Does BMI work for children?
Not with these categories. Children and teens use BMI-for-age percentiles on growth charts.
Sources
- WHO Technical Report Series 894 (2000) — Obesity: preventing and managing the global epidemic
- CDC — Adult BMI categories
- Wikipedia — Body mass index
Reviewed Oct 17, 2026 · test vectors fixtures/calculators/health/bmi-calculator/