How this calculation works
This circumference method estimates body density from tape measurements and converts density to a body-fat percentage. It implements the legacy Hodgdon-style equations reproduced in the cited research, not a scan and not a current military eligibility assessment. Small differences in tape placement can change the estimate substantially.
Worked example
This example uses illustrative inputs. Your current result is shown above.
For the male equation with height 175 cm, waist 85 cm and neck 38 cm, waist − neck = 47 cm. D = 1.0324 − 0.19077 × log10(47) + 0.15456 × log10(175) ≈ 1.06009785. Body fat = 495 ÷ 1.06009785 − 450 ≈ 16.938%, displayed as 16.9%.
Assumptions and limits
- All measurements must be centimetres. Converting only height while leaving circumferences in inches changes the logarithms and produces an invalid estimate.
- The logarithm inputs must be positive: waist must exceed neck for the male equation; waist plus hip must exceed neck for the female equation.
- Tape measurements and population-based body-density equations introduce uncertainty. This result is not a diagnosis, a laboratory body-composition measurement or certification against a service’s current standards.
Questions people ask
Why is hip circumference needed only for the female equation?
The two empirical equations use different predictors and constants. Hip enters the female waist-plus-hip-minus-neck term; the male equation does not use it.
Can I enter inches directly?
No. These coefficients are for centimetres. Multiply every inch measurement by 2.54 before entering it, or use the unit converter.
Is this the same as a body-fat scan or an official Navy assessment?
No. It is a legacy tape-measure estimate. Scans and official assessments can use different protocols, eligibility rules and measurement procedures.