Adult body mass index estimate

BMI Calculator

Calculate adult BMI from height and weight, then see the BMI category, healthy weight range for your height, BMI Prime, and Ponderal Index. The result updates instantly as you type.

BMI is a screening measure. It should be considered with other health information, not used as a diagnosis.

Reference table

Adult BMI Categories

For adults age 20 and older, CDC categories use the same BMI cutoffs regardless of age, sex, or race.

BMI Category	BMI Range	Plain-English note
Underweight	Less than 18.5	May indicate low body weight for height.
Healthy Weight	18.5 to less than 25	Common adult healthy-weight screening range.
Overweight	25 to less than 30	Higher than the healthy-weight screening range.
Class 1 Obesity	30 to less than 35	Falls within CDC obesity class 1.
Class 2 Obesity	35 to less than 40	Falls within CDC obesity class 2.
Class 3 Obesity	40 or greater	Also described by CDC as severe obesity.

How to Use This BMI Calculator

Choose U.S. units or metric units.
Enter height and weight. The result updates automatically.
Review BMI, adult BMI category, healthy weight range, BMI Prime, and Ponderal Index.
If the user is age 2 through 19, use a child and teen BMI percentile tool instead of fixed adult cutoffs.

BMI Formula

U.S. units

BMI = 703 x weight in pounds / height in inches squared.

Metric units

BMI = weight in kilograms / height in meters squared.

BMI Prime

BMI Prime = BMI / 25. It shows how your BMI compares with the upper end of the adult healthy-weight range.

When BMI Is Useful and When It Is Limited

BMI is useful as a quick screening number because it needs only height and weight. It can help adults compare a result with common BMI categories and decide whether a conversation with a health care professional may be useful.

BMI is not a direct body-fat measurement. It may be less informative for athletes, people with high muscle mass, older adults, pregnant people, and anyone whose body composition or medical history changes the meaning of a height-weight number.

Data Sources and Medical Disclaimer

This page uses adult BMI categories and interpretation notes from U.S. public-health sources. It is not a substitute for professional medical advice, diagnosis, or treatment.

CDC adult BMI categories CDC child and teen BMI categories NHLBI BMI calculator notes

Editorial Review

Reviewed for source alignment

The calculator was reviewed by the CalcToolBox editorial team for formula clarity, category wording, source references, and health disclaimer placement.

Last updated

July 6, 2026. Adult BMI categories were checked against CDC BMI category guidance.

Scope

This tool estimates adult BMI only. It does not calculate child BMI percentiles, diagnose health status, or recommend a treatment plan.

BMI Calculator FAQ

How do I calculate BMI?

BMI is calculated as weight in kilograms divided by height in meters squared. In U.S. units, BMI equals 703 times weight in pounds divided by height in inches squared.

What is a healthy BMI for adults?

For adults age 20 and older, CDC categories define healthy weight as a BMI from 18.5 to less than 25. BMI is a screening measure, not a diagnosis.

Does BMI work for children and teens?

Children and teens ages 2 through 19 use BMI-for-age percentiles instead of the fixed adult BMI cutoffs. This calculator is intended for adults and shows a warning when age is under 20.

Why can BMI be misleading?

BMI uses only height and weight. It does not measure muscle mass, bone density, body fat percentage, pregnancy status, waist size, or individual medical risk.

What is BMI Prime?

BMI Prime compares your BMI with 25, the upper end of the common adult healthy-weight range. A BMI Prime below 1 is below 25, while a BMI Prime above 1 is above 25.

What is Ponderal Index?

Ponderal Index is weight divided by height cubed. It is another height-weight index that can be useful as a comparison, especially at very short or very tall heights.

Is this BMI calculator medical advice?

No. This calculator is for general informational use only. Talk with a qualified health care professional for personal medical guidance.

CalcToolBox provides simple health and fitness calculators for general informational use. Verify results with a qualified professional before making health decisions.