How to use the Body Fat Percentage
- Measure height, then neck circumference just below the larynx.
- Measure waist at the navel for men, at the narrowest point for women.
- Women also measure hips at the widest point.
- Measure first thing in the morning, unclothed, keeping the tape snug but not compressing.
How the calculation works
The Navy formula relates log-transformed circumference differences to body density, then converts density to fat percentage. It works because fat deposits at the waist while the neck stays comparatively lean, so the gap between them tracks adiposity. Men use waist minus neck; women add hips, since female fat distribution loads the hips and thighs as well as the abdomen.
Expect roughly ±3 to 4 percentage points against a DEXA scan, with the method less accurate at the extremes — very lean and very obese individuals both drift. Its real strength is consistency: measured the same way each time, the trend is reliable even if the absolute number is not. Healthy ranges run about 10 to 20% for men and 18 to 28% for women, with essential fat around 3% and 12% respectively.
Men: %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76 ; Women: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387 (inches)Source: US Navy circumference method (Hodgdon and Beckett, Naval Health Research Center).
Worked example
A man 70 inches tall with a 36-inch waist and a 15.5-inch neck.
- waist − neck = 20.5; log₁₀(20.5) = 1.3118.
- 86.010 × 1.3118 = 112.83.
- log₁₀(70) = 1.8451; 70.041 × 1.8451 = 129.24.
- %BF = 112.83 − 129.24 + 36.76 = 20.35.
About 20.4% body fat — at the upper edge of the healthy range for men, and a figure to track monthly rather than daily.
Frequently asked questions
How accurate is the tape method?+
Within about 3 to 4 percentage points of a DEXA scan for most people, and less accurate at very low or very high body fat. Measured consistently, the trend is more useful than the absolute figure.
What is a healthy body fat percentage?+
Roughly 10 to 20% for men and 18 to 28% for women, varying with age. Athletes often sit below those ranges; essential fat is around 3% for men and 12% for women.
Why does the women's formula include hips?+
Female fat distribution loads the hips and thighs as well as the abdomen, so waist alone underestimates total fat. Including hips corrects for that pattern.
When should I measure?+
First thing in the morning before eating or drinking, unclothed, with the tape snug but not compressing tissue. Same time, same conditions, every time.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.