BMI Calculator

Adult BMI calculator

Use US customary units or metric units to calculate body mass index for adults age 20 and older. The result includes the adult BMI category, the weight range corresponding to BMI 18.5 through 24.9 at the entered height, BMI Prime, and the Ponderal Index.

Adult BMI categories

The CDC adult BMI categories classify BMI below 18.5 as underweight, 18.5 to less than 25 as healthy weight, 25 to less than 30 as overweight, and 30 or greater as obesity. Obesity is further described as Class 1 from 30 to less than 35, Class 2 from 35 to less than 40, and Class 3 at 40 or greater.

BMI formulas

With metric units, divide weight in kilograms by height in meters squared. With US customary units, divide weight in pounds by height in inches squared and multiply by 703. The CDC lists both formulas in its BMI frequently asked questions.

BMI = weight (kg) / height (m)^2

BMI = 703 x weight (lb) / height (in)^2

Worked example

An adult who is 5 feet 10 inches tall and weighs 160 pounds has a BMI of about 23.0. That value is within the CDC healthy-weight screening category for adults. At 70 inches tall, BMI 18.5 through 24.9 corresponds to approximately 129 to 174 pounds.

BMI Prime and Ponderal Index

BMI Prime divides BMI by 25, the upper boundary of the CDC healthy-weight category. A BMI Prime of 0.92 corresponds to a BMI of 23. The Ponderal Index divides weight in kilograms by height in meters cubed; it is another height-and-weight ratio, not a diagnosis.

BMI limitations

BMI is a screening measure, not a direct measurement of body fat and not a diagnosis. The CDC adult BMI calculator guidance says BMI should be considered with medical history, health behaviors, physical findings, and laboratory findings. Muscle mass, body composition, pregnancy, and other factors can affect interpretation. Discuss health concerns with a qualified healthcare professional.

Children and teens

Do not interpret this adult result for anyone younger than 20. CDC guidance uses sex- and age-specific BMI percentiles for children and teens ages 2 through 19.

BMI is a height-weight screening value, not body fat percentage. The body fat calculator provides separately labeled adult circumference and BMI-based predictions, with measurement and population limits.

Frequently asked questions

What is a healthy adult BMI?

The CDC healthy-weight screening category for adults is BMI 18.5 to less than 25. Individual health cannot be determined from BMI alone.

Does sex change the adult BMI formula?

No. CDC adult BMI categories apply regardless of age, sex, or race for adults age 20 and older, although those factors may affect how BMI relates to body composition and health.

Is this medical advice?

No. This calculator provides a mathematical screening result and cannot diagnose a condition or recommend treatment.