BMI Home > Calculate BMI

The only measurements you need to determine BMI are a person's height and weight. It is calculated the same way for adults and children, but the criteria for interpreting the outcomes are different. You can calculate BMI by using the simple formula explained in the following article. The version of the formula you use to determine BMI differs, depending on which system of measurement you're using.

Calculating BMI

Research on obesity has shown that body fat can be assessed using a calculation called body mass index, or BMI. BMI does not measure body fat directly, but it correlates closely to direct measures of body fat in most people.
The only measurements needed to calculate BMI are a person's height and weight. Because of this, BMI is an inexpensive and easy-to-use method of screening for weight categories that may lead to health problems (see Health Effects of Obesity).

What's the Formula Used to Calculate BMI?

BMI is calculated the same way for adults and children. This calculation is based on the following formulas, depending on whether you are using the metric system or the English system.
(Click BMI Calculator for another assessment method.)
Metric System
The formula when using this system is:
Weight in kilograms divided by height in meters squared (weight (kg) / [height (m)2]).
Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters before you use the formula.
To calculate BMI, take the weight (kg) and divide it by height (m). Then divide that number once again by height (m). Round to the second decimal place.
An example of calculating BMI using the body mass index formula:
Height = 165 cm (1.65 m)
Weight = 68 kg
BMI Calculation: 68 ÷ (1.65)2 = 24.98
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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