Body fat percentage is a better fitness signal than weight or BMI alone, because it separates fat mass from lean mass. The US Navy method below estimates it using a few tape measurements — neck, waist, and (for women) hips — combined with height. The NIH still considers body fat percentage a more useful clinical signal than BMI for active adults.
How the US Navy body fat formula works
For men: %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. For women: %BF = 163.205 × log₁₀(waist + hips − neck) − 97.684 × log₁₀(height) − 78.387. All measurements are in centimeters. The method is accurate to about ±3% versus DEXA scans for most adults.
Worked example
A man 175 cm tall with a 38 cm neck and 85 cm waist: %BF ≈ 16.7%.
