Complete guide: BMI
Updated:
BMI is weight in kilograms divided by height in meters squared. Conversion uses 1 pound = 0.45359237 kg and 1 inch = 2.54 cm, so both systems yield the same index.
For adults age 20+, CDC categories are underweight below 18.5, healthy weight 18.5 to less than 25, overweight 25 to less than 30 and obesity from 30. This is a screening indicator, not a diagnosis or direct body-fat measurement.
Muscle, body composition, age, ethnicity and medical circumstances affect interpretation. These categories are not applied to children, pregnancy or cases requiring individual evaluation. Sources reviewed 2026-10-24.
How it works
- 1Enter weight and height in the chosen system.
- 2BMI = kg ÷ (cm/100)².
- 3Interpret the category as reference, not diagnosis.
Frequently asked questions
Can children or pregnant people use it?
No. This general adult estimate does not replace pediatric, prenatal or nutritional assessment or an individualized clinical plan.
Does BMI measure body fat?
It does not distinguish fat and muscle; clinical context and other measurements are needed.
Are values preserved when sharing?
The link retains entered values. Weight, dates and other health data are included in the link: share only with people you want to see them.