How to Calculate Your Body Mass & Fat Percentage

Knowing how to calculate your body mass and fat percentage is an excellent way to measure the success and effectiveness of your exercise or weight-loss program. Without accurate biometric data, there is no way to truly determine if your current program is producing positive results. Learning to calculate your BMI and fat percentage is the first step toward establishing a healthy and effective diet or exercise routine, and the steps below provide you with the information you need to begin.

Things You'll Need

• Bathroom scale
• Yardstick
• Cloth tape measure
• Calculator

Instructions

1. Know the terminology. Your body mass index, or BMI, is the ratio of the square of your height to your weight. BMI does not take into account fat-to-muscle ratio, which means your BMI number should be used in combination with other biometric data to ensure accuracy. Fat percentage is calculated by taking measurements, in centimeters, of five body areas, and using that information to determine the estimated percentage of fat on your body. This formula requires measurements to be made with an accuracy of 0.5 cm, and the formula differs for men and women.

2. Weigh yourself, without clothing, on your bathroom scale. Record this number on a sheet of paper.

3. Measure your height using the yardstick. Multiply the number of inches by itself in order to determine the square of your height, and record this number on your sheet of paper, next to your height.

4. Divide your weight by the square of your height. Multiply the result by 703 in order to calculate your BMI. A calculator should be used in order to obtain accurate results.

5. Wrap the tape measure around your abdominal area. For men, this measurement should be taken at the level of the belly button. For women, the measurement should be taken at the thinnest section of the waist. Record this information on your sheet of paper.

6. Snugly wrap the tape measure around the largest circumference of the hips. (This measurement is for women only.) Tthe tape should not compress the skin or create an indentation. Write down this figure, as it is also needed to determine your body fat percentage.

7. Measure the neck, inferior to the larynx. The tape should slope slightly downward in the front, and the fit should be snug. (This measurement is for both genders.) Record your result.

8. Using the measurements you've taken of the various areas of your body, as well as your height, plug your figures into the appropriate body-fat-percentage formula, and use your calculator to determine your body fat percentage. For men, the formula is:%Fat=495/(1.0324-0.19077(log(waist-neck))+0.15456(log(height)))-450For women, the formula is:%Fat=495/(1.29579-0.35004(log(waist+hip-neck))+0.22100(log(height)))-450.

9. Discuss your calculations with your doctor, nutritionist or fitness trainer before beginning any exercise or diet program.