When determining your BMI, the only two pieces of information you need are a person's weight and height measurements. Because BMI can be calculated so simply and inexpensively, it is a popular method for healthcare professionals and the general public to use as a way of screening for weight categories that may lead to health problems.
Calculating BMI: An Overview
Recent research on obesity has shown that a relatively accurate measure of body fatness can be made using a calculation known as body mass index, or BMI for short. BMI does not measure body fat directly but 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 the calculation requires only these two simple measurements, it is considered the most inexpensive and easy method to screen for weight categories that may lead to health problems (see Health Effects of Obesity).
Specifics on How Your BMI is Calculated
BMI is calculated the same way for both adults and children. The BMI calculation is based on the following formula depending on whether you are using the metric system or the English system.
(Click on the BMI Calculator to determine your BMI.)
If you're using the metric system, the BMI formula 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