BMI Calculator
Calculate adult body mass index from height and weight using pounds and feet plus inches, or kilograms and centimeters. The result includes an adult category and a height-based healthy weight range.
BMI Calculator tool
About the BMI Calculator
Use BMI as a screening reference when discussing weight with a clinician, not as a direct measurement of body fat. Results are estimates and not medical advice.
How Is BMI Calculated?
The equations below describe the calculation. Use the units specified in each expression; display rounding is not used to assign BMI categories.
BMI = weight (kg) / height (m)^2
BMI = 703 × weight (lb) / height (in)^2
Healthy weight (kg) = 18.5 to 24.9 × height (m)^2
Example
At 70 kg and 175 cm, BMI = 70 / 1.75² = 22.9, in the healthy adult category.
How to Use the BMI Calculator
- Choose US customary or metric units.
- Enter your height; in US units, use whole feet and remaining inches from 0 to less than 12.
- Enter your current weight in pounds or kilograms.
- Read the live result and calculation breakdown; correct any validation messages.
- Use Reset to restore the sample values, or copy the result for discussion with a clinician.
BMI Calculator Examples
Metric adult example
At 70 kg and 175 cm, BMI is 22.9 and the BMI 18.5–24.9 weight range is 56.7–76.3 kg.
Higher BMI example
At 100 kg and 180 cm, BMI is 30.9, in obesity class I.
Interpreting BMI
Consider BMI alongside waist size, blood pressure, laboratory findings, and health history.
Measurement and limitations
Measure height without shoes and use a consistent weight measurement. Pregnancy and conditions affecting body size or fluid balance can make BMI misleading.
Frequently Asked Questions
Who can use adult categories?
The adult categories shown apply at age 20 and older. Younger people need sex- and age-specific BMI-for-age percentiles.
What are the adult cutoffs?
Underweight is below 18.5; healthy is 18.5 to below 25; overweight is 25 to below 30; obesity is 30 or higher. Classification uses the unrounded value.
What do obesity classes mean?
Class I is BMI 30 to below 35, class II is 35 to below 40, and class III is 40 or higher.
Can athletes have a high BMI?
Yes. BMI does not distinguish muscle from fat, so muscular people may have a high BMI without high body fat.
Is the healthy range a weight prescription?
No. It is a screening reference calculated with BMI 18.5–24.9, not a personalized treatment goal.
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