An accurate calculation of BMI can be obtained using the body mass index formula. The same result can also be arrived at using a special calculator or chart -- these methods do the math for you. Regardless of which method you use, the only measurements needed to calculate BMI are a person's height and weight.
BMI Calculation: An Overview
Researchers studying obesity have determined that a person's level of body fat can be measured using a simple calculation known as body mass index (BMI). While BMI is an indirect measure of body fat, it does correlate closely to direct measures of body fat in most people.
The only measurements needed to calculate BMI are height and weight. As a result, this is an inexpensive and easy way for healthcare providers and the general public to screen for weight categories that may lead to health problems (see Health Effects of Obesity).
How to Calculate BMI
BMI calculation is done the same way for both adults and children. The formula differs somewhat, depending on whether you are using the metric system or the English system.
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.
Then, take the weight (kg) and divide it by height (m). Divide that number once again by height (m). Round to the second decimal place.
For example: Height = 165 cm (1.65 m), Weight = 68 kg
BMI calculation: 68 ÷ (1.65)2 = 24.98