How this calculator works
The Hodgdon-Beckett US DoD circumference equations use logarithms of tape measurements, converted to inches. This adult field method is not valid in pregnancy and can differ from measured body fat by several percentage points. Keep the tape level and use a consistent protocol: the male abdominal site is at the navel, the female waist at the natural waist, and female hip at the widest circumference. The sheet supplies no fitness category thresholds, so no fitness classification is invented. The result is an estimate for information only and is not medical advice.
Formula
Male %BF = 86.010 log10(waist - neck) - 70.041 log10(height) + 36.76. Female %BF = 163.205 log10(waist + hip - neck) - 97.684 log10(height) - 78.387. All lengths in inches.
Worked example
A male at 70 in with a 15 in neck and 36 in waist has an estimated 21.3% body fat.
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Frequently asked questions
Why does hip appear for men?
The shared form shows it, but the male equation ignores hip and accepts male calculations without a hip value.
Is this a direct measurement?
No. Tape placement, body shape and the population used to derive the equations affect the estimate.
What if the tape measurements are rejected?
The male equation needs the waist to be larger than the neck, and the female equation needs waist plus hip to exceed the neck, because the logarithm requires a positive value.