Body fat calculator
Estimate your body fat from your height and a few tape measurements. The equations are the US Navy’s, fitted on hundreds of sailors in 1984. Add your weight to split it into fat and lean mass.
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Where to measure
Use a soft tape, keep it level and snug without pressing into the skin, and measure twice. Men measure the abdomen at the level of the navel and the neck. Women measure the waist at its narrowest, the hips where the buttocks stick out most, and the neck.
The equations
Hodgdon and Beckett’s reports give body density from the measurements in centimetres, and Siri’s 1961 formula turns density into a percentage:
Men: density = 1.0324 − 0.19077 × log10(abdomen − neck) + 0.15456 × log10(height)
Women: density = 1.29579 − 0.35004 × log10(waist + hips − neck) + 0.22100 × log10(height)
Body fat % = 495 ÷ density − 450
Many websites print a version in inches with coefficients such as 86.010. Neither Navy report contains it, and away from typical measurements it drifts from the original, so this calculator converts inches to centimetres and uses the reports' own equations.
How far to trust it
The men’s equation was fitted on 602 men with a typical error of about 3.5 percentage points, the women’s on 214 women with about 3.7. That is too loose for comparing yourself with a friend and good enough for following your own change, as long as you measure the same way each time. More in how to estimate body fat with a tape measure.
Sources
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center report 84-11, 1984.
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center report 84-29, 1984.
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