Body Fat Calculator: Navy Circumference Method

How this body fat percentage calculator works

This calculator uses the circumference method developed by James Hodgdon and Marcie Beckett in 1984, often called the Navy body fat method. It estimates body density relationships from height and selected tape measurements rather than measuring fat directly. For men, the equation is%BF = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76. For women, it is%BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. Every length in these equations is in inches, and “log10” means the base-10 logarithm, not the natural logarithm. Metric measurements are divided by 2.54 before calculation.

The men’s coefficients come from Hodgdon JA, Beckett MB. NHRC Technical Report 84-11 (1984)(Circumference-based body-fat equations for men; DTIC ADA143890.). The women’s coefficients come fromHodgdon JA, Beckett MB. NHRC Technical Report 84-29 (1984)(Circumference-based body-fat equations for women; DTIC ADA146456.). Keeping those two reports separate matters because the inputs and coefficients differ. Weight does not appear in either percentage equation. If you supply optional weight, EVR simply multiplies weight by the estimated percentage to show approximate fat mass, then subtracts that amount from weight to show approximate lean mass.

Worked examples

For a man who is 70 inches tall with a 16-inch neck and 34-inch abdomen, the substituted calculation is 86.010 × log10(34 − 16) − 70.041 × log10(70) + 36.76. That produces approximately15.49% body fat. For a woman who is 65 inches tall with a 14-inch neck, 28-inch waist, and 38-inch hip, the calculation is 163.205 × log10(28 + 38 − 14) − 97.684 × log10(65) − 78.387. The result is approximately 24.58% body fat. The live substituted formula above lets you verify which measurements entered the calculation instead of presenting the output as a black box.

How to take repeatable measurements

Use a flexible, non-stretch tape and keep it level rather than angled around the body. The tape should touch the skin without compressing it. Stand normally, avoid deliberately pulling the abdomen inward, and record measurements at a consistent point in the breathing cycle. Follow the sex-specific measurement sites described by the source method: the abdomen measurement used for men and the waist and hip measurements used for women are not interchangeable labels. Take two or three readings and repeat any pair that differs substantially. Measuring at a similar time of day can reduce variation from meals, hydration, and temporary abdominal distension.

The sensitivity panel shows why consistency matters. It recalculates the estimate with waist changed by one inch, neck changed by half an inch, and, for women, hip changed by one inch in each direction. These are not confidence intervals. They are nearby-input comparisons that show how tape-reading differences propagate through the logarithmic formula.

What the result can and cannot tell you

Circumference equations are convenient because they require only a tape, but convenience is not the same as direct observation. The estimate may differ from results produced by skinfold assessment, bioelectrical impedance, imaging, or laboratory methods. It can also fit some body shapes better than others because the equations were derived from particular study samples. A change in the result can reflect a real change in body composition, measurement noise, or both. For personal tracking, use the same tape, locations, technique, and conditions, then focus on trends across multiple readings rather than a single decimal value.

A waist measurement that is no greater than the neck measurement cannot produce a meaningful men’s estimate, so the calculator displays a soft warning. It also flags percentages outside a broad plausible range. A warning is an invitation to check tape placement, entries, and units; it is not a diagnosis. Do not use this number alone to make medical, nutrition, eligibility, or performance decisions.

Responsible use and Navy-method disclaimer

This page provides a historical Hodgdon and Beckett circumference estimate for general fitness planning. It is not medical advice and is not an official Navy Body Composition Assessment, current service policy, pass/fail decision, or eligibility determination. EVR does not apply current Navy standards or tables. If body-composition changes could affect a health condition, pregnancy, medication, eating-disorder recovery, or military requirement, consult the appropriate clinician or authorized official.

Sources

• Hodgdon JA, Beckett MB. NHRC Technical Report 84-11 (1984) — Circumference-based body-fat equations for men; DTIC ADA143890.
• Hodgdon JA, Beckett MB. NHRC Technical Report 84-29 (1984) — Circumference-based body-fat equations for women; DTIC ADA146456.

Frequently asked questions