Body Fat Calculator (U.S. Navy Method)
Estimate your body fat percentage with a tape measure — the U.S. Navy formula from height, neck, waist and (for women) hip.
An estimate from body measurements with the U.S. Navy formula; individual errors of several percentage points are normal. It is not a medical assessment — talk to a doctor about your own health and weight.
About this tool
Measure your neck, waist and — for women — hips with a tape measure, then enter them with your height and weight. The calculator estimates your body fat percentage with the U.S. Navy circumference equations (Naval Health Research Center, 1984) and shows your fat mass and lean mass. Works in centimetres or inches. For adults; an estimate, not a medical assessment.
Frequently asked questions
Researchers at the Naval Health Research Center (Hodgdon and Beckett, 1984) fitted equations that predict body density from circumferences and height; Siri’s equation (495 ÷ density − 450) turns that into percent fat. For men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450, in cm. A man of 180 cm with a 38 cm neck and 90 cm waist gets 19.8%.
Neck: just below the Adam’s apple. Waist: for men at the level of the navel, for women at the narrowest point of the waist. Hips (women only): at the widest point of the buttocks, feet together. Keep the tape level and snug without pressing into the skin, and measure height without shoes.
In the original studies the equations were compared with underwater weighing. The standard error was 3.5 percentage points for 602 Navy men and 3.7 points for 214 Navy women, and 2.7 (men) and 4.0–4.4 (women) in cross-validation groups. So for about two in three people, a result of 25% means the true value lies between roughly 21% and 29%.
Fat mass is your weight × body fat percentage; lean mass is everything else — muscle, bone, organs and water. A woman of 65 kg with 29.4% body fat has 19.1 kg fat mass and 45.9 kg lean mass. Measuring the same way every few weeks shows the trend better than a single result.
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