What is body fat percentage?
Body fat percentage is the proportion of your total body weight made up of fat tissue. Someone weighing 80kg with 20% body fat carries 16kg of fat and 64kg of lean mass — muscle, bone, water, and organs. It is a far more useful indicator of health and body composition than weight or BMI alone.
BMI uses only height and weight and cannot distinguish between fat and muscle. A muscular person can have a high BMI with very low body fat. Body fat percentage cuts through this by measuring what actually matters.
How the US Navy formula works
Women: % fat = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
The formula uses circumference measurements rather than direct fat assessment. For men it uses height, neck, and waist. For women it adds hip circumference. Accuracy is ±3–4 percentage points when measurements are taken correctly.
Body fat category reference
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athlete | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
How to measure accurately
Measurement consistency matters more than the formula itself. Always measure at the same time of day (morning is best), after a normal exhale, with the tape horizontal and not pulled tight. Take three readings and use the average. The biggest source of error in this method is inconsistent waist measurement placement.
Frequently asked questions
Further reading
Body fat percentage and bodyweight tell different stories. To connect your body fat result to a calorie plan, start with the TDEE calculator to find your maintenance calories, then use the calorie deficit calculator to build a timeline. For the protein intake that preserves lean mass during fat loss, read how much protein you need to build muscle.