Body fat percentage consists of essential body fat and storage body fat. Calculation of body fat percentage is not always an exact science, but it has improved vastly over the years. Many methods are used to calculate body fat percentage, and all have some margin of error. Additionally, all calculations of body fat percentage are estimates and not direct measures.
Step 1
Use a reliable body fat calculation measure. Hydrostatic weighing is considered the gold standard, but it is very expensive. Skinfold calipers are the most practical, easy and cost-effective way to perform body fat calculations. If done correctly, body fat percentage calculation using skinfold calipers has a margin of error rate of 2 to 5 percent.
Step 2
Perform a three-site measurement twice on the right side of the body. When performing the pinching for measurements on either a male or female, use your index finger and thumb to pinch and pull the skin. The calipers should be placed roughly 1 cm away from your thumb and index finger. Maintain your pinch of the skin while reading the caliper measurement. Your goal is to separate the skin from the muscle. On males, the sites for measurements will be the chest using a diagonal pinch fold, abdominals using a vertical pinch fold and the thigh using a vertical pinch fold. For females, it will be the triceps using a vertical fold pinch, the suprailiac using a diagonal fold pinch and the thigh using a vertical fold pinch.
Step 3
Input the sum of the three site measurements into a body density equation. You will need to input the person's age into the equation as well. The most common body density equations used are the ones referenced in the Volume 40, 1978 British Journal of Nutrition by researchers Jackson and Pollock:
Men: Body density = 1.10938 - (0.0008267 x sum of chest, abdomen and thigh skinfolds) + (0.0000016 x square of the sum of chest, abdomen and thigh) - (0.0002574 x age).
Women: Body density = 1.0994921 - (0.0009929 x sum of triceps, thigh and suprailiac skinfolds) + (0.0000023 x square of the sum of triceps, thigh and suprailiac skinfolds) - (0.0001392 x age in years).
Step 4
Input the number for body density into the Siri equation. In the textbook "Techniques for Measuring Body Composition," Siri and colleagues use a two-compartment model for body fat percentage calculation. The calculation is Body fat = (4.95 / body density) - 4.50. Working this equation will give you the final number for body fat percentage.
References
- "British Journal of Nutrition;" Generalized Equations for Predicting Body Density of Men; A. Jackson and M. Pollock; 1978
- "Techniques for Measuring Body Composition;" W. Siri, J. Brozek and A. Hanschel; 1961
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