Estimate body fat % from tape measurements using the US Navy method. See your category, fat mass, and lean mass — no calipers or gym required.
Added May 17, 2026
Input
Measure at the navel (narrowest point for women).
Measure just below the larynx, sloping slightly downward.
Used to calculate fat mass and lean mass in kg.
Result
Enter a value for biological sex to see your result.
Estimates body fat percentage using the U.S. Navy circumference method — no calipers or DEXA scan needed. Just a tape measure and a few body measurements give you fat %, category, and optionally fat and lean mass.
Male: %BF = 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450 Female: %BF = 495 / (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
log₁₀(85 − 38) = log₁₀(47) ≈ 1.672; log₁₀(175) ≈ 2.243. Denominator ≈ 1.060 → 495/1.060 − 450 ≈ 17.0% (Fitness category).
Inputs
Result
log₁₀(75 + 98 − 33) = log₁₀(140) ≈ 2.146; log₁₀(165) ≈ 2.217. Denominator ≈ 1.035 → 495/1.035 − 450 ≈ 28.5% (Average category).
Inputs
Result
The Navy method is accurate to within roughly ±3–4 percentage points of DEXA (gold-standard) scanning for most adults. It is more accurate than BMI for assessing body composition but less accurate than hydrostatic weighing or DEXA. Measurement consistency matters more than single-reading precision.
Waist: measure horizontally at the navel for men; at the narrowest point for women. Neck: just below the larynx (Adam's apple), tapering slightly downward — do not suck in. Hip (women only): the widest point around the buttocks. Use a flexible, non-stretch tape and keep it level.
ACE (American Council on Exercise) categories: Men — Essential fat 2–5%, Athletes 6–13%, Fitness 14–17%, Average 18–24%, Obese ≥25%. Women — Essential fat 10–13%, Athletes 14–20%, Fitness 21–24%, Average 25–31%, Obese ≥32%.
BMI uses only height and weight, so it cannot distinguish muscle from fat — a muscular athlete and an out-of-shape person can have identical BMI. The Navy method uses circumference measurements that correlate with fat distribution, giving a more meaningful body-composition estimate.
The Navy formula was developed and validated for adults aged 18+. For adolescents, different reference norms apply. Consult a paediatrician or use age-specific standards.