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.

Lean body mass calculator: weight minus fat mass

Lean body mass is your weight minus your fat mass: everything in the body that is not fat, including muscle, bone, water, and organs. Some sources reserve the term fat-free mass for weight minus all fat and use lean body mass for a figure that includes a small amount of essential fat. This page uses the simple definition, weight minus estimated fat mass, which some sources call “fat-free mass.” Enter your weight in the optional field to see it next to estimated fat mass.

The calculation has two steps. Fat mass = weight × body fat % ÷ 100. Lean body mass = weight − fat mass, which is the same as weight × (1 − body fat % ÷ 100). At 180 lb and 20% body fat, fat mass is 36.0 lb and lean body mass is 144.0 lb. At 70 kg and 25% body fat, fat mass is 17.5 kg and lean body mass is 52.5 kg. Results use the unit of the weight you enter.

The result inherits the error of the tape-measure body fat estimate. At 180 lb, a body fat percentage that is 3 points off moves lean body mass by 5.4 lb (180 × 3 ÷ 100), in the opposite direction to fat mass. Compare readings taken the same way over time rather than relying on one number.

Some lean body mass calculators predict lean mass from height and weight alone. This page does not use those formulas. It starts from the body fat percentage estimated from your tape measurements, so fat mass and lean mass always add up to the weight you entered before rounding.

To compare fat-free mass across people of different heights, the FFMI (fat-free mass index) calculator divides it by height squared. Enter the body fat percentage from this page with your weight and height.

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.

For the current Army standard, which uses a waist-to-height ratio rather than a body fat percentage, see the Army body fat calculator.

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