Body Fat Calculator (US Navy Method)
Estimate body fat percentage using the US Navy circumference method. Just a tape measure required — accurate within ±3-4% for most people.
This calculator is for informational purposes only and does not constitute medical advice. Results are estimates based on general formulas. Consult a qualified healthcare professional before making health decisions.
Body fat percentage is a far more useful metric than weight or BMI for body composition. The US Navy method uses a tape measure and three (or four) circumference measurements to estimate it — accurate enough for tracking progress without spending money on DEXA scans.
How the Navy method works
For men, the formula uses height, neck, and waist circumferences (all in inches): 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women, hip circumference is added: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. The log10 transformation captures the non-linear relationship between body shape and fat percentage.
When to use this calculator
Use it to track body composition changes over weeks and months — far more meaningful than the bathroom scale, which fluctuates with water weight, glycogen, and food in your gut. Measure first thing in the morning, after the bathroom, before food. Keep tape measure technique consistent — same spots, same tension, same time of day.
Worked example
A 5'10" (70 inch) man, 36-inch waist, 15-inch neck. Body fat = 86.010 × log10(36 − 15) − 70.041 × log10(70) + 36.76 = 86.010 × 1.322 − 70.041 × 1.845 + 36.76 ≈ 113.7 − 129.2 + 36.76 = 21.3%. That's in the "average" range. Dropping the waist to 33 inches (still 5'10", 15-inch neck) brings body fat to about 16% — fitness range.