Reference formulas and worked examples below keep their stated units. Monetary examples use USD; dimensional examples use US customary units unless labeled otherwise. Metric calculator inputs are converted to these reference units before calculation. Choosing another currency does not convert example amounts or exchange money.
How to use this body fat calculator
Choose the equation, enter height and circumferences, and add weight for the fat-mass estimates. This is a circumference estimate, not a body scan or military eligibility test.
How the calculation works
Using inches, male percentage = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76.
Female percentage = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. Metric measurements are converted to inches before evaluating these equations.
Fat mass = body weight × percentage/100. Fat-free mass = body weight − fat mass. Logs and intermediate values keep full calculation precision; display rounding is not a service-specific assessment procedure.
Worked example
For the male equation with height 70 in, abdomen 34 in and neck 15 in, the estimate is approximately 17.5%. At 165 lb, that corresponds to about 28.9 lb of estimated fat mass and 136.1 lb of fat-free mass.
Limits and assumptions
A legacy adult circumference estimate with individual error; not a diagnosis, direct body-composition measurement, ideal-weight target or current military compliance assessment. Does not model pregnancy, children, unusual body composition or population-specific validation. Results outside 0–100% are rejected rather than clamped.
Frequently asked questions
Should I measure waist the same way for both equations?
No. The male equation uses abdomen at navel level; the female equation uses the natural waist plus hip circumference. Follow the selected field labels.
Is this a current military body-composition test?
No. It applies published legacy equations without service-specific rounding, standards or eligibility decisions.
Is fat-free mass the same as muscle?
No. It also includes water, bone, organs and other non-fat tissue.
Can I compare small changes over time?
Measurement error and tape placement can exceed small changes. Keep the measuring method consistent and do not treat the result as a precise scan.
References
US Army: published legacy circumference equations (2019)
National Academies: military body-composition assessment methods