What is BMI and how is it calculated?
Learn the BMI formula, work through an example and understand how adult results are interpreted and limited.
Body mass index, or BMI, relates a person’s weight to their height. It is widely used as a quick screening measure, not as a medical diagnosis or a direct measurement of body fat.
The metric formula is:
BMI = weight (kg) / height (m)^2For 75 kg and 1.72 m:
75 / 1.72^2 = 25.35For most adults, that result falls in the overweight category:
| BMI | Adult category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0 or above | Obesity |
BMI’s advantage is that it requires only two easy measurements. Its limitation is that it cannot separate muscle from fat, locate body fat or describe overall health. Athletes, older adults and people with unusual body composition need additional context. Children and teenagers use age- and sex-specific percentiles; pregnancy also requires different interpretation.
Use the BMI calculator to calculate the value and an adult reference range. Combine it with weight history, waist size, fitness and clinical information.