BMI Calculator
Calculate adult BMI, weight category, healthy-weight range, BMI Prime and Ponderal Index from metric or US measurements. Enter your values below to calculate instantly, then use the explanation and example to understand the result.
Enter your values
Understanding your BMI result
Body mass index (BMI) compares weight with height. For adults age 20 and older, the CDC groups BMI into underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9) and obesity (30.0 or higher). Obesity is commonly divided into class I (30.0–34.9), class II (35.0–39.9) and class III (40.0 or higher).
The calculator above shows your category on a visual scale, a healthy-weight range for the entered height, BMI Prime and Ponderal Index. These extra values provide context, but BMI remains a screening measure rather than a diagnosis.
BMI formula
US units: BMI = 703 × weight (lb) ÷ height² (in²)
Adult BMI categories
| Category | BMI |
|---|---|
| Underweight | < 18.5 |
| Healthy weight | 18.5–24.9 |
| Overweight | 25.0–29.9 |
| Obesity class I | 30.0–34.9 |
| Obesity class II | 35.0–39.9 |
| Obesity class III | 40.0+ |
Healthy weight range
For adults, this tool also calculates the weights that correspond to BMI 18.5 through 24.9 at the height you entered. This is a mathematical reference range, not a personalized target. A clinician may consider medical history, body composition, blood pressure, laboratory results, medications, pregnancy status and other factors.
Limitations of BMI
BMI does not directly measure body fat and cannot distinguish fat mass from muscle or bone. Two people with the same BMI can have different body composition and health risks. Athletes, older adults and people at the extremes of height may need additional context. Children and teens should be assessed with age- and sex-specific BMI-for-age percentiles rather than adult cutoffs.
Sources and review basis
Category definitions and interpretation guidance are aligned with the U.S. Centers for Disease Control and Prevention (CDC) adult BMI guidance. Formula definitions are standard BMI equations. Content last reviewed: September 4, 2026.
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What is a healthy BMI for adults?
For most adults, the standard healthy-weight BMI range is 18.5 to 24.9.
Does BMI measure body fat?
No. BMI is calculated from height and weight. It can be useful as a screening measure, but it is not a direct body-fat measurement.
Can children use this adult BMI calculator?
Adult BMI categories should not be used to classify children and teens. Pediatric BMI uses age- and sex-specific percentiles.
Why does the calculator show a healthy-weight range?
It converts the standard adult healthy BMI interval back into a weight interval for the height entered, giving useful context around the BMI number.