Body Density Calculator

How it is calculated

The tool applies a Jackson-Pollock style quadratic equation to the skinfold sum S (millimetres) and age A (years). Men: density = 1.10938 − 0.0008267·S + 0.0000016·S² − 0.0002574·A. Women: density = 1.0994921 − 0.0009929·S + 0.0000023·S² − 0.0001392·A. Density is shown in g/cc and then converted with the Siri equation, body fat % = 495 ÷ density − 450. Anything other than female is treated as male. A sum of zero or less, an age of 0 or below or above 130, a density outside 0.9–1.15, or a fat figure at or below 0 % or above 75 % shows no result. The equation is quadratic, so it is only trustworthy for realistic sums; it is an estimate, not a lab density.

Common mistakes

• Entering a single skinfold or the sum of a different number of sites. The coefficients are fitted to one particular multi-site sum, so a one-site value reads as a very lean person.
• Using the male setting for a woman. The same 60 mm and age 30 gives 17.95 % for a man but 24.13 % for a woman because the constants differ.
• Entering the sum in centimetres. The equation works in millimetres, so 6 instead of 60 gives a near-zero body fat.
• Trusting very low sums. A sum of 5 mm prints 1.00 % body fat, which no real person has, so treat extreme values with suspicion.
• Pushing the sum to several hundred millimetres. The quadratic bends back (300 mm gives 46.17 %, 400 mm only 32.00 %), so very large sums are outside what it can model.