The US Navy developed this method so sailors’ body composition could be estimated anywhere with nothing but a tape measure. For men it uses waist minus neck against height; for women it adds the hip measurement. Validated against underwater weighing and DEXA, it typically lands within a few percentage points — good enough to track change over time, which is what body fat numbers are really for. Measurement technique decides accuracy: neck at the narrowest point just below the Adam’s apple, waist at the navel, relaxed and not pulled in, hip at the widest point, tape snug but not compressing the skin.
A note on health results: every figure this tool gives is an estimate from a standard formula — it is not medical advice and it does not diagnose anything. Bodies vary, and formulas cannot see your health history. Use the result as a starting point, and consult a clinician or registered dietitian for personal health decisions.
How to use it
Pick your sex and unit — cm or inches; women get the extra hip field.
Enter your height — cm, or feet and inches.
Measure and enter neck and waist — plus hips for women; measure on bare skin, tape level all the way round.
Add your weight (optional) — to split your weight into fat mass and lean mass.
What you get
The genuine Navy formulas — log-based, sex-specific, exactly as published.
Standard categories — essential, athletes, fitness, average and obese ranges for your sex.
Fat mass & lean mass — with your weight entered, see what the percentage means in kilos.
Sense checks built in — impossible measurements get a clear explanation, not a nonsense number.
Frequently asked questions
How accurate is the Navy method?
Studies comparing it with DEXA scans and hydrostatic weighing generally find it within about 3–4 percentage points for most people. It is less reliable at the extremes of leanness or obesity, and sloppy tape placement is the biggest source of error — measure the same way, at the same time of day, each time.
What is a healthy body fat percentage?
For men: 6–13% is the athletic range, 14–17% fitness, 18–24% average, 25% and above obese; 2–5% is essential fat, the minimum the body needs. For women the ranges run higher — 14–20% athletic, 21–24% fitness, 25–31% average, 32%+ obese, with 10–13% essential.
Where exactly do I measure my waist?
At the level of your navel, standing relaxed, at the end of a normal breath out — not sucked in, and not after a big meal if you want consistent readings. Keep the tape horizontal and snug without digging in.