BMI Calculator
Calculate body mass index (BMI) from height and weight using metric or US customary units. For adults age 20 and older, the result includes the BMI value, CDC adult screening category and a height-based weight range corresponding to BMI 18.5 through 24.9. BMI is a screening measure rather than a diagnosis and does not directly measure body fat.
BMI = weight in kilograms ÷ height in meters².
How to use the BMI Calculator
- Choose metric or US customary units and enter an adult age of 20 years or older.
- Enter height and weight. US measurements are converted internally to metric units before the BMI formula is applied.
- BMI is calculated as weight in kilograms divided by height in meters squared.
- The result is matched to the CDC adult BMI categories: underweight below 18.5, healthy weight from 18.5 to below 25, overweight from 25 to below 30, and obesity at 30 or higher.
- The displayed healthy-weight range reverses the BMI formula using the entered height and BMI values from 18.5 through 24.9.
- BMI should be interpreted as one screening measure among other health information rather than as a diagnosis or direct measurement of body composition.
Examples
BMI using metric units
An adult weighing 70 kg at 1.75 m tall has BMI = 70 ÷ 1.75², which is approximately 22.9.
BMI using pounds and feet
When pounds and feet/inches are entered, the calculator converts them to kilograms and centimeters before applying the same metric BMI equation.
Healthy-weight range
For a selected height, the calculator rearranges the BMI equation to estimate the weights corresponding to BMI 18.5 and 24.9.
Frequently asked questions
What is BMI?
Body mass index is weight in kilograms divided by height in meters squared. It is widely used as a screening measure of weight relative to height.
What are the CDC adult BMI categories?
For adults age 20 and older, BMI below 18.5 is underweight, 18.5 to below 25 is healthy weight, 25 to below 30 is overweight, and 30 or higher is obesity. Obesity is further divided into three classes.
Is BMI a diagnosis?
No. BMI is a screening measure. Individual health assessment can also involve medical history, physical findings, laboratory results, body composition and other factors.
Does BMI measure body fat?
No. BMI is calculated only from height and weight. People with different muscle, bone and fat composition can have the same BMI.
Can this calculator be used for children?
No. This page intentionally uses adult categories for people age 20 and older. Children and teens require age- and sex-specific BMI percentiles and growth charts.
Why does the calculator show a weight range?
The range is the mathematical weight corresponding to adult BMI values from 18.5 through 24.9 at the entered height. It is not an individualized medical target.
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