Body fat calculator
Body fat percentage and lean mass from neck, waist and hip measurements — the US Navy tape method.
A 1984 regression from the US Naval Health Research Center that estimates body fat from tape measurements alone, with no analyser involved. It is well known because the US Department of Defense uses it for body composition standards. The trade-off is an error band of roughly ±3–4 percentage points, wider for very muscular builds and for people who carry weight only at the abdomen — a series of measurements taken the same way is worth more than any single number.
Tape measurements
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Uses waist and neck.
Narrowest point below the larynx.
Men: widest at navel height. Women: narrowest point of the waist.
Composition
Body fat
16.9%
Lean mass
58.1 kg
Fat mass
11.9 kg
How to measure
Keep the tape level with the floor, measure after breathing out, snug without compressing the skin. Measuring first thing in the morning makes days comparable.
The error band is roughly ±3–4 percentage points, wider for very muscular builds and for weight carried only at the abdomen.
An estimate from tape measurements; it does not replace body composition testing. Not medical advice.
Height 175 cm, neck 38 cm, waist 85 cm gives 16.9%
The male formula takes waist minus neck and height as base-10 logarithms: 495 ÷ (1.0324 − 0.19077·log(waist−neck) + 0.15456·log(height)) − 450. Those values give 16.9%. At 70 kg, lean mass is 70 × (1 − 0.169) = 58.1 kg and fat mass is the remaining 11.9 kg. The female formula uses waist plus hip minus neck with different coefficients — height 165 cm, neck 34 cm, waist 75 cm and hip 95 cm give 26.4%.
One centimetre of waist moves the result by 0.7–0.8 points
Weight is not in the formula. The percentage is set by the circumferences and height; weight only turns it into kilograms. In the example above, a waist of 80 cm gives 12.9% and 90 cm gives 20.7%. The neck works the other way: 36 cm gives 18.5%, 40 cm gives 15.4%. Measuring on an inhale or with the tape tilted feeds that difference straight into the number.
Why there is no band
The regression was fitted to the builds of 1984 US Navy personnel, so an individual carries a ±3–4 point margin. A reading of 16.9% means somewhere between roughly 13% and 21%. Drawing lines inside that margin and naming them would give a label that flips on one centimetre of tape. The value is a statistically estimated position, not a medical diagnosis.
Common questions
QWhere exactly do I measure?
Neck: the narrowest point below the larynx. Waist: for men, the widest point at navel height; for women, the narrowest point of the waist. Hip: the widest point. Keep the tape level with the floor, measure after breathing out, and pull it snug without compressing the skin. Measuring first thing in the morning makes days comparable.
QIt disagrees with my bioimpedance scale — which is right?
Both are estimates. Bioimpedance follows body water, so it moves by a few percentage points depending on how much you have drunk or whether you have just trained. The tape method ignores water but cannot see differences in build. If you need an accurate figure, DEXA is the reference; otherwise pick one method and repeat it under the same conditions.
QChanging my weight does not change the percentage — is that right?
Yes. Weight is not in the formula. At 16.9%, 70 kg gives 58.1 kg of lean mass and 75 kg gives 62.3 kg — only the kilograms move.
QWhy is there no hip field for men?
Because the male equation in the original report uses only waist and neck. The female equation uses waist plus hip. Switching sex changes both the coefficients and the fields.