Health Atlas tool
BMI Calculator for Adults
Calculate your Body Mass Index in U.S. or metric units, then use the result as one screening reference — not a diagnosis.
Calculate your BMI
This calculator uses the adult reference categories for ages 20 and older.
BMI at a glance
For adults, BMI is weight relative to height. It is a screening measure that should be considered alongside other health information.
- Adult categories here apply from age 20 onward.
- People with the same BMI can have different body composition and health histories.
- If a result raises a personal concern, discuss it with a qualified clinician.
Adult BMI chart: the reference categories
This BMI chart uses the WHO adult classification. Find your number in the right-hand column to see which range it falls into. These labels are screening references, not an individual diagnosis — two people with the same BMI can have very different body composition and health.
See the full BMI chart for women by height.
| Classification | BMI (kg/m²) |
|---|---|
| Severe thinness | Less than 16 |
| Moderate thinness | 16 to less than 17 |
| Mild thinness | 17 to less than 18.5 |
| Normal range | 18.5 to less than 25 |
| Overweight | 25 to less than 30 |
| Obese class I | 30 to less than 35 |
| Obese class II | 35 to less than 40 |
| Obese class III | 40 or greater |
How the calculation works
Metric: BMI = weight (kg) ÷ height (m)²
U.S. customary: BMI = 703 × weight (lb) ÷ height (in)²
Reference weight range: the weight produced by BMI values of 18.5 and 25 at your entered height.
BMI Prime: your BMI ÷ 25. Ponderal Index: weight (kg) ÷ height (m)³.
How to use the result
The result is useful as a starting point for a conversation or for tracking a change over time using the same measurement method. It cannot tell how much of a person’s weight is muscle, fat, bone, or water, and it does not replace individual clinical assessment. The added indicators are mathematical views of the same height-and-weight inputs; they add context, not a diagnosis.
BMI calculator FAQ
Can BMI diagnose a health condition?
No. BMI is a screening measure and cannot diagnose a condition on its own.
Why does this calculator ask for age?
These adult categories are intended for people age 20 and older. Children and teens need age- and sex-specific BMI interpretation.
Does BMI measure body fat?
No. BMI is calculated from height and weight; it does not directly measure body fat or body composition.