Body Fat Calculator
Estimate adult body-fat percentage with a circumference equation commonly called the U.S. Navy method. The calculator also shows a separate BMI-based estimate, fat mass and lean mass so the two models are not confused.
Estimate only: tape placement, hydration, body shape and the selected equation profile can materially change the result. This is not a diagnosis, a scan, a fitness qualification or a current military compliance test.
Body-fat formulas used
Measurements are converted to inches before applying the circumference equations:
- Male profile: % body fat = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76.
- Female profile: % body fat = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387.
- BMI estimate: 1.20 × BMI + 0.23 × age − 10.8 × S − 5.4, where S is 1 for the male profile and 0 for the female profile.
Fat mass equals body weight multiplied by the circumference percentage. Lean mass is the remainder. The calculator does not average the two percentage estimates because their assumptions and errors differ.
Six checked examples
| Inputs | Circumference result | BMI estimate |
|---|---|---|
| Male profile; 80 kg, 180 cm, neck 40 cm, waist 90 cm, age 35 | 18.46%; fat mass 14.77 kg | 21.48% |
| Female profile; 65 kg, 165 cm, neck 34 cm, waist 78 cm, hip 98 cm, age 32 | 29.74%; fat mass 19.33 kg | 30.61% |
| Male profile; 70 kg, 175 cm, neck 38 cm, waist 82 cm, age 25 | 14.54%; lean mass 59.82 kg | 16.98% |
| Female profile; 75 kg, 170 cm, neck 36 cm, waist 85 cm, hip 105 cm, age 45 | 34.22%; lean mass 49.33 kg | 36.09% |
| Male profile; 95 kg, 185 cm, neck 42 cm, waist 105 cm, age 50 | 26.26%; fat mass 24.95 kg | 28.61% |
| Female profile; 55 kg, 160 cm, neck 31 cm, waist 70 cm, hip 90 cm, age 28 | 24.24%; fat mass 13.33 kg | 26.82% |
How to measure and interpret the estimate
- Use a flexible tape on bare skin or thin clothing, keep it level, and take measurements after a normal exhale.
- Repeat each measurement two or three times. A small tape-location change can shift the calculated percentage.
- The male equation uses height, neck and waist. The female equation also uses hip circumference.
- Values outside 2%–70% are rejected as implausible for this model; a rejected value usually indicates a measurement or profile problem.
- DEXA, air-displacement plethysmography and professionally performed skinfold measurements use different methods and will not necessarily agree.
Sources and method limits
- Hodgdon JA and Beckett MB (1984), Naval Health Research Center circumference-and-height prediction reports for men and women. The equations here are historical estimation models, not a statement of current service policy.
- Deurenberg P, Weststrate JA and Seidell JC (1991), Body mass index as a measure of body fatness: age- and sex-specific prediction formulas.
- CDC: BMI is a screening measure and does not directly measure body fat.
Related calculators: BMI Calculator, Calorie Calculator and Percentage Calculator.
Questions
Is this the same as an Army or Navy fitness test?
No. It uses a commonly published circumference equation for an educational estimate. Current service-specific rules, measurement sites, rounding and qualification standards can differ and can change.
Why are there two estimates?
The circumference method uses tape measurements. The BMI method uses weight, height, age and the selected equation profile. Disagreement is expected; neither result is a direct scan.
Can I use this for children or pregnancy?
No. The calculator intentionally accepts adults only and is not designed for pregnancy, children, athletes with unusual body composition or clinical decisions.
Does a lower result always mean better health?
No. Body fat is only one measurement, and extremely low values can also be harmful. Interpretation belongs in the context of health history, symptoms, performance and professional advice.
Track scale change separately
Body-fat estimates and scale weight answer different questions. Use the Weight Loss Percentage Calculator to calculate percentage lost or gained, progress toward a weight goal and an optional average weekly change.