Body Fat Percentage Calculator (US Navy Method)
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
Body fat percentage is estimated with the US Navy method, from neck and waist measurements (and hip measurement for women) relative to height. For a 178 cm tall man with a 38 cm neck and an 85 cm waist, the estimated body fat is about 16.5%.
Explanation
The US Navy method (developed by Hodgdon and Beckett to assess military fitness) estimates body fat percentage from simple tape-measure readings, with no specialized equipment: neck circumference, waist circumference, and, for women, hip circumference, related to height through a logarithmic formula. Unlike BMI (see our BMI calculator), which doesn't distinguish fat mass from muscle mass using just weight and height, this method gives a more specific estimate of body composition: two people with the same BMI can have very different body fat percentages depending on their muscle mass. This method remains an estimate, less precise than a direct measurement (bioelectrical impedance, DEXA scan, skinfold calipers), but its margin of error (typically around 3 to 4 percentage points compared to a reference measurement) is reasonable for personal tracking over time, as long as you always measure in the same spots and under similar conditions (in the morning, fasted, for example) — the trend then matters more than the absolute value.
Example: a man, 178 cm tall, 38 cm neck, 85 cm waist
Inputs
Sex: male. Height: 178 cm. Neck: 38 cm. Waist: 85 cm.
Calculation
Body fat = 86.010 × log₁₀((85 − 38) ÷ 2.54) − 70.041 × log₁₀(178 ÷ 2.54) + 36.76 ≈ 16.5% (the formula, calibrated in inches, converts the measurements from centimeters before using them).
Result
The estimated body fat for this profile is about 16.5%.
Frequently asked questions
Why is the formula different for men and women?
Typical body fat distribution differs between men and women (more around the abdomen in men, more around the hips in women), which led the method's authors to calibrate two separate formulas from different body measurements: neck and waist for men, neck, waist, and hips for women.
Is this estimate as accurate as a lab measurement?
No: it's an estimate from a statistical formula, not a direct measurement. Methods like DEXA scanning or professional bioelectrical impedance are more accurate, but require specialized equipment. The US Navy method remains useful for regular personal tracking thanks to its simplicity (just a tape measure), as long as you always measure the same way.
What if the result seems off or doesn't show up?
First check your measurements: the formula assumes the waist is clearly larger than the neck (for men), or that waist plus hips clearly exceeds the neck (for women). A measurement or entry error that reverses this relationship makes the calculation mathematically impossible (the logarithm of a negative number), and no result can be shown — retake the measurements rather than reading a missing result as a value of zero.