Body fat percentage is the share of your total bodyweight that is fat tissue, as opposed to lean tissue like muscle, bone, organs, and water. For a 200-pound person at 20 percent body fat, 40 pounds is fat and 160 pounds is fat-free mass.
The full picture
Body fat is not all the same. Essential fat sits inside organs, nerves, and bone marrow and is non-negotiable for life. Below 3 percent body fat in men and 12 percent in women, hormonal and immune problems appear quickly. Storage fat lives subcutaneously and in visceral depots and is what cutting and bulking phases change.
Healthy ranges depend on sex. Men. 3 to 5 percent essential, 6 to 13 percent athletic, 14 to 17 percent fit, 18 to 24 percent average, 25-plus percent obese. Women. 12 percent essential, 14 to 20 percent athletic, 21 to 24 percent fit, 25 to 31 percent average, 32-plus percent obese. Women carry more essential fat for reproductive function.
Measurement methods differ in cost, access, and accuracy. DEXA is the practical gold standard, available at sports clinics for $50 to $150 per scan. Hydrostatic weighing and BodPod are similarly accurate but rarer. Skinfold calipers (Jackson-Pollock 3 or 7 site) cost $10 and give 3 to 4 percent error in trained hands. Bioelectrical impedance (BIA)is fast but heavily affected by hydration. Navy method uses tape measurements and gives 3 to 5 percent error. RFM (Relative Fat Mass) uses height and waist for a quick approximation.
How it is calculated
Navy method (men). BF% = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. Navy method (women). BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. Jackson-Pollock uses 3 or 7 skinfold sites fed into a body density equation, then Siri's formula converts density to percent body fat.
Common misconceptions
- The bathroom scale's body fat reading is not measuring fat. It is measuring electrical resistance through your body and inferring fat. Hydration, meals, and skin temperature shift it by several percent.
- "Visible abs" is not a fixed body fat percentage. Genetic ab structure, ab thickness, and skin thickness vary. Some men show abs at 15 percent. Others need 9 percent.
- Body fat percentage is not the only health marker. Two people at 20 percent body fat can have very different visceral fat distributions and metabolic profiles.
Citations
- Jackson AS, Pollock ML. (1978). Generalized equations for predicting body density of men. Br J Nutr, 40, 497-504.
- Hodgdon JA, Beckett MB. (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center.
- Woolcott OO, Bergman RN. (2018). Relative fat mass (RFM) as a new estimator of whole-body fat percentage. Sci Rep, 8, 10980.