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
Men: % fat = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
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
Body fat percentage ranges
| 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
What is a healthy body fat percentage?
For men, the fitness range of 14–17% is optimal for health and performance. Average healthy is 18–24%. For women, fitness range is 21–24%, average healthy is 25–31%. Essential fat minimums — below which health is compromised — are 3–5% for men and 10–13% for women.
How accurate is the US Navy body fat formula?
Accurate to within 3–4 percentage points for most people when measurements are taken correctly. This is sufficient for tracking progress and categorising body composition. Accuracy decreases for very muscular individuals and those with unusual fat distribution. DEXA scan (available at many gyms and clinics) remains the gold standard.
How often should I measure body fat?
Once every 4–6 weeks gives enough time for meaningful change and reduces noise from day-to-day fluctuations. Always measure under the same conditions — same time of day, same state of hydration. Track the trend over time rather than fixating on individual readings.
What is the difference between body fat percentage and BMI?
BMI uses only height and weight and cannot distinguish between fat and muscle. Body fat percentage directly measures what proportion of your body weight is fat tissue. A muscular athlete can have an "obese" BMI while having excellent body fat levels. Body fat % is the more meaningful metric for body composition tracking.
Disclaimer: Body fat estimates using the US Navy circumference method are accurate to within 3–4 percentage points for most people. Results are for informational purposes only and are not a substitute for clinical body composition assessment or medical advice.