How to Calculate BMI
Many people don't know how to calculate BMI (body mass index). Although the formula is the same for both adults and children, it does differ slightly depending on whether you use the metric or English system. If you want to calculate BMI without using the formula, you can use a body mass index calculator or chart.
Calculating BMI: An Introduction
Body mass index (BMI) is an indirect measure of a person's body fat. The formula is the same for adults and children, as well as with different genders and ethnicity. However, the BMI formula does differ slightly depending on whether you are using the metric system or the English system.
How to Calculate BMI Using the Metric System
If you're using the metric system, you can learn how to calculate BMI by using the following formula:
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.
An example of calculating BMI using the formula: Height = 165 cm (1.65 m), Weight = 68 kg
BMI Calculation: 68 ÷ (1.65)2 = 24.98
Calculate BMI Using the English System
With the English system, the BMI formula is:
Weight in pounds (lbs) divided by height in inches (in) squared and multiplied by a conversion factor of 703 (weight (lbs) / [height (in)2] x 703).
Therefore, to calculate BMI, take the weight (lbs) and divide it by height (in). Take the result of that calculation and divide it by height again. Then, multiply that number by 703. Round to the second decimal place.
An example of calculating body mass index using the BMI formula: Weight = 150 lbs, Height = 5'5" (65 inches)
BMI Calculation: [150 ÷ (65)2] x 703 = 24.96
(If you want to learn how to calculate BMI using another method, click BMI Calculator or BMI Chart. Also, click BMI and Weight for more information on what other factors healthcare providers consider when determining a person's risk for certain medical conditions related to weight.)