BMI Calculator Guide
Updated September 2026
What is BMI?
Body mass index (BMI) is a screening measure based on weight relative to height. For adults, the standard formula is weight in kilograms divided by height in meters squared.
For adults 20 and older, CDC categories are: below 18.5 underweight, 18.5 to 24.9 healthy weight, 25.0 to 29.9 overweight, and 30 or greater obesity. BMI is a screening measure and should be considered with other health information rather than used by itself to diagnose a condition.
How to calculate BMI
Convert your weight to kilograms and height to meters, then use: BMI = weight (kg) ÷ height² (m²).
Example: 70 kg and 1.75 m gives a BMI of about 22.9.
What BMI does not tell you
BMI does not directly measure body fat, muscle mass, fitness, waist circumference, medical history, or how fat is distributed. A healthcare professional can interpret BMI alongside those factors.