Body Fat Calculator (Navy)
Estimate your body fat percentage with the US Navy tape method, plus fat mass, lean body mass and category.
Measure with a soft tape, relaxed and unflexed: neck just below the larynx, waist at the navel (men) or the narrowest point (women), hips at the widest point. Results update as you type.
- Body fat
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- Category
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- Fat mass
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- Lean body mass
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These numbers are an estimate from a tape measure, not a medical measurement and not medical advice. The Navy method is typically within about 3–4 percentage points of a DEXA scan and can be off by more for very lean, very muscular or pregnant people. Talk to a doctor or a registered dietitian before acting on the result.
How it works
This calculator uses the US Navy circumference (tape) method, the
Hodgdon–Beckett equations, in their metric form. For men it needs your height, neck and waist;
for women it also needs your hip measurement. The formulas are:
%fat = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
for men, and
%fat = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
for women, with every length in centimetres. Imperial entries are converted to centimetres
first and run through the same metric equation, so metric and imperial always agree with each
other (a published inches-only variant of the formula can differ by around a tenth of a point).
A worked example: a man 180 cm tall with a 38 cm neck and an 85 cm waist gets 495 ÷ (1.0324 − 0.19077 × log₁₀(47) + 0.15456 × log₁₀(180)) − 450 = 16.1 % body fat. Add your weight and the tool splits it into fat mass and lean body mass, and places you on the American Council on Exercise category scale (essential fat, athletic, fitness, acceptable, obese — the bands are different for men and women).
Everything is computed in your browser with plain JavaScript. Your measurements are never uploaded, stored or sent anywhere, there is no sign-up and there are no ads. Measure at the same time of day, on bare skin, with the tape snug but not compressing, and track the trend over weeks rather than obsessing over a single reading.
Frequently asked questions
How does the US Navy body fat formula work?
It is the Hodgdon-Beckett circumference (tape) method. For men, body fat % = 495 / (1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)) - 450, with every length in centimetres. For women the hip measurement is added: 495 / (1.29579 - 0.35004 x log10(waist + hip - neck) + 0.22100 x log10(height)) - 450. Example: a man 180 cm tall with a 38 cm neck and an 85 cm waist gets 16.1 % body fat. Imperial entries are converted to centimetres and run through the same equation, so metric and imperial always agree.
What is a healthy body fat percentage?
Using the American Council on Exercise bands, men fall into essential fat 2-5 %, athletic 6-13 %, fitness 14-17 %, acceptable 18-24 % and obese 25 % or more. For women the same bands are essential fat 10-13 %, athletic 14-20 %, fitness 21-24 %, acceptable 25-31 % and obese 32 % or more. Women naturally carry more essential fat, which is why the scales differ. The calculator places your result on the right scale for you.
How accurate is the tape measure method?
It is an estimate, typically within about 3-4 percentage points of a DEXA scan for average builds, and less reliable for very lean, very muscular or pregnant people. Accuracy depends almost entirely on your tape work: measure on bare skin, relaxed and unflexed, with the tape snug but not compressing, the neck just below the larynx, the waist at the navel for men or at the narrowest point for women, and the hips at the widest point. Measure at the same time of day and watch the trend over weeks rather than a single reading. It is not medical advice.