Body Fat Calculator (Navy Method)
The U.S. Navy method estimates body fat percentage from tape measurements you can take at home — neck, waist, and (for women) hips, plus height. It needs no calipers or scanning equipment, and its repeatability makes it ideal for tracking change over time.
Fill in the fields above to see your result.
How it's calculated
The Navy method, developed at the Naval Health Research Center by Hodgdon and Beckett in 1984, predicts body density from body circumferences and converts it to body fat percentage. For men the formula uses the waist-minus-neck girth and height: %fat = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women it uses waist plus hip minus neck: %fat = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.221 × log10(height)) − 450. All measurements are in centimeters.
The logic is anatomical: the waist (and hip) circumference tracks fat storage, while the neck circumference acts as a proxy for frame size and lean mass, so their difference isolates fatness from bigness. Against underwater weighing — the reference method of its era — the Navy equations predict within roughly ±3-4% for most people, comparable to consumer bioimpedance scales but far more repeatable, since tape positions don't fluctuate with hydration the way electrical measurements do.
Measurement technique decides your accuracy. Measure the neck just below the larynx, the waist at the navel (relaxed, not sucked in), and hips at their widest point, with the tape snug but not compressing skin. Take each measurement twice and average. The absolute number matters less than the trend: measure the same way every few weeks and the direction of change is trustworthy even where the level is off by a few points. Very muscular or very lean individuals should expect the estimate to read a little high.
Frequently asked questions
How accurate is the Navy body fat method?
Within roughly ±3-4% of reference methods for most people — similar to consumer bioimpedance scales, but more repeatable because tape measurements don't swing with hydration.
Where exactly do I measure?
Neck just below the larynx, waist at the navel while relaxed, hips (women) at the widest point. Tape snug but not compressing. Measure twice and average.
What is a healthy body fat percentage?
Roughly 10-20% for men and 18-28% for women covers the fit-to-average range. Athletes run lower; essential fat floors are about 3% for men and 12% for women.
Why does my result differ from my smart scale?
Bioimpedance scales are highly sensitive to hydration, food, and time of day. Neither method is exact — pick one, measure consistently, and track the trend.
Take it with you
Every calculator, plus workout and macro tracking, in the ElevenSix Fitness app for iPhone.