What a circumference estimate tells you
The Navy equations use body proportions to estimate fat percentage. They are inexpensive and repeatable with care, but a tape measure does not directly distinguish fat from muscle, bone, or organs.
The Navy body-fat equations
All lengths are converted to inches before applying base-10 logarithms. The male equation uses abdomen at the navel minus neck. The female equation uses natural waist plus hip minus neck. These are sex-specific population estimates.
How to use this calculator
- 1Choose the equation and enter your height.
- 2Measure the neck just below the larynx without compressing the skin.
- 3Use abdomen at the navel for the male equation; use natural waist and widest hip circumference for the female equation.
- 4Keep the tape level and measure relaxed after a normal exhale; repeat to check consistency.
Understanding your result
Use the percentage as an approximate reference, especially when tracking measurements with the same technique. Small changes can reflect tape placement or normal variation rather than a real change in body fat.
Assumptions & limitations
- The method was developed in military populations and may fit athletes, older adults, or other body types poorly.
- Pregnancy, abdominal distension, and inconsistent tape placement can invalidate the estimate.
Frequently asked questions
Where should I measure my waist?+
For the male Navy equation, use the abdomen at the navel. For the female equation, use the natural waist and also measure the widest part of the hips.
Why is a hip measurement only used in one equation?+
The original equations use different body-shape predictors. Adding or removing a measurement would no longer reproduce the selected method.
Will this match a DEXA scan?+
Not necessarily. Circumference equations and DEXA use different methods and both have limitations; their estimates are not interchangeable.
What if the calculator rejects my measurements?+
Check units, tape positions, and whether the circumference combination is valid for a logarithm. Some body proportions also fall outside a plausible range for this equation.
