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The Fitties Blog

How to Calculate Body Fat with the Body Mass Index (BMI) Body Fat Formula

April 03, 2023 | Lifestyle and Wellness

The Body Mass Index (BMI) formula is the most popular and widely-used method for measuring body fat in men and women. Through this method of calculation, body mass can be estimated, thus giving a decent understanding of an individual’s overall health. BMI is a measure of estimated body composition based on height and weight ratios. Using a Body Mass Index calculator, which are widely available online, users simply input the height and weight of the individual being measured. The calculated result can then be plugged into a BMI chart, which will provide an estimate the body composition of the individual.

The Body Mass Index chart has four categories. Depending upon the calculation of an individual’s BMI, their body composition will fall into one of these categories, which will provide a better understanding of their level of fitness. The four Body Mass Index categories are:

Underweight = < 18.5

Normal weight = 18.5–24.9

Overweight = 25–29.9

Obese = 30 >

The medical and fitness community has already begun to reevaluate the Body Mass Index method and reconsider if it is a proper method for understanding and individual’s health. The simplicity of the method make it appealing to the masses, but results might not be the most reliable or accurate for most people. Since a basic calculation is the foundation of the method, BMI does not take into consideration different body types or body styles, such as athletes or individuals with high levels of fitness. As a result, many find results to be misconstrued. Still, BMI remains one of the most prevalent methods for measuring body fat. 

If you would like to try calculating your body fat using the Body Mass Index method, below are the formulas for males and females, in both pounds/inches and kilograms/centimeters. Otherwise, in the current version of FatCaliper+, which you can download now and start using for free, Body Mass Index is automatically included as part of the calculation results of all methods.

Males & Females (pounds/inches)

Measure the following: Height, Weight (in lbs)

Body Mass Index = (Weight in pounds / (Height in inches x Height in inches) ) x 703

Males & Females (kilograms/centimeters)

Measure the following: Height, Weight (in kg)

Body Mass Index = (Weight in kilograms / (Height in centimeters x Height in centimeters) )

BMI Categories

Underweight = <18.5

Normal weight = 18.5–24.9

Overweight = 25–29.9

Obese = BMI of 30 or greater

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