What BMI measures

Body mass index compares weight with height. The metric formula is weight in kilograms divided by height in meters squared. The US formula multiplies weight in pounds by 703, then divides by height in inches squared.

Common adult reference ranges

For adults, commonly used screening ranges are below 18.5, 18.5–24.9, 25–29.9, and 30 or higher. These labels are population-level screening categories, not a diagnosis.

Important limitations

BMI does not directly measure body fat, fitness, bone density, or fat distribution. Muscular people, older adults, pregnant people, and some ethnic groups may need different context. Adult ranges should not be used for children or teenagers.

Check the units with an example

An adult who weighs 70 kg and is 1.75 m tall has BMI = 70 ÷ (1.75 × 1.75), or about 22.9. Entering 175 as meters rather than centimeters, or mixing pounds with the metric formula, produces a meaningless result. Use a recent measurement, remove heavy items when appropriate, and record the unit with the value. Small day-to-day weight changes do not necessarily represent a meaningful change in health.

Interpret the result as screening information

The CDC adult BMI categories apply to adults age 20 and older and describe BMI as one potential health indicator to consider with other factors. Children and teens require age- and sex-specific growth references. A clinician may consider medical history, waist measurement, body composition, medications, pregnancy, nutrition, activity, and laboratory findings. The calculator cannot determine an individual diagnosis, ideal weight, treatment, or health risk from height and weight alone.

This calculator is educational and is not medical advice. Discuss health concerns with a qualified healthcare professional.