Body Fat Percentage Calculator — US Navy Method

The US Navy body-fat method was developed by James Hodgdon and Marcia Beckett at the Naval Health Research Center in 1984. They measured neck, waist, and hip circumferences on hundreds of Navy personnel, then validated those measurements against hydrostatic (underwater) weighing — the gold standard at the time. The resulting regression formulas give a body-fat estimate from a tape measure alone, with a standard error of roughly ±3.7 percentage points for men and ±3.6 for women.

The formulas in metric (centimetres) are:

• Men: %BF = 495 / (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450
• Women: %BF = 495 / (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450

The 495 / x − 450 structure is the Siri equation, which converts an estimated body density into a fat-fraction percentage. The circumference regression sits inside the Siri shell — Hodgdon and Beckett fitted the coefficients so that the predicted density best matched the hydrostatic readings. The same body-fat number can also be obtained from a separate imperial-units log₁₀ regression published in the same Navy reports; the calculator above runs both and shows the imperial cross-check inline, so you can see how close the two curves stay.

Once the percentage is known, two derived numbers follow directly. If you provide your weight, fat mass is weight × body-fat fraction, and lean body mass is the remainder (weight × (1 − body-fat fraction)). The category badge uses the American Council on Exercise reference table — essential fat, athletes, fitness, average, and obese bands — published in their certified personal trainer materials and widely used by ACSM-certified practitioners.

The method has known limitations. Tape measurements depend on posture, tape tension, exact placement, and how recently you ate or drank. Body shape that differs sharply from the original Navy cohort — for example very muscular necks, post-pregnancy abdomens, or extreme abdominal obesity — pushes the regression beyond the range it was fitted on. Treat the output as a screening estimate, not a clinical diagnosis. For comparison, DEXA scans have a typical error of ±1–2 percentage points, BodPod ±2–3, and skin-fold callipers in trained hands ±3.

• Hodgdon & Beckett (1984) — Prediction of percent body fat for U.S. Navy men (NHRC Report 84-11)
• Hodgdon & Beckett (1984) — Prediction of percent body fat for U.S. Navy women (NHRC Report 84-29)
• OPNAVINST 6110.1J — Navy Physical Readiness Program (body composition assessment procedure)
• American Council on Exercise — Percent body fat norms (men and women)
• ACSM's Guidelines for Exercise Testing and Prescription, 11th ed. — reference body-composition tables

Formulas and classification bands were last cross-checked against the NHRC reports and ACE tables on 2026-05-11. The page is reviewed annually and whenever any of these bodies publishes updated guidance.