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.
Limits and assumptions
The estimate uses the US Navy circumference formulas: for men 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76, and for women 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387, with metric inputs converted to inches first and the result shown to one decimal place. The hip measurement is used for women only.
No result is shown if the waist is not larger than the neck (the logarithm is undefined) or if the formula returns a value at or below 0% or above 60%, which usually means a measurement was typed in the wrong units. Tape placement matters more than the formula; the method does not account for age, bone density or unusually muscular or very lean builds.
Frequently asked questions
What is the US Navy body fat formula?
For men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. All measurements in inches.
How accurate is the US Navy method?
Within ±3-4% body fat compared to DEXA scan for most people, which is good enough for tracking progress. It's less accurate at extremes — very lean (<8% men, <15% women) or very high body fat — but excellent for the typical range.
What body fat percentage is healthy?
Men: 10-20% is generally healthy; 6-13% is athletic. Women: 18-28% is healthy; 14-20% is athletic. Below ~5% (men) or ~13% (women) is essential fat — going lower is dangerous and not sustainable.
Why does the female formula include hip measurement?
Women carry proportionally more fat in the hips and thighs (gluteofemoral fat). Including hip measurement makes the formula far more accurate for women than waist + neck alone.