Free body fat percentage calculator using the U.S. Navy method. Estimate body fat from neck, waist, and hip circumference measurements — no special equipment needed.
The U.S. Navy body fat method estimates body fat percentage from simple tape measurements rather than calipers or lab equipment. It uses neck and waist measurements for men, and neck, waist, and hip measurements for women, along with height.
Developed for military body-composition screening, it is a practical option when you want a quick estimate with only a measuring tape. It is less direct than lab methods, but it is easy to repeat under the same conditions.
The formula uses sex-specific logarithmic equations because circumference patterns differ between men and women.
This worksheet is useful when you want a quick body-fat estimate without calipers or scan access. It works well for repeated trend checks, especially if you measure at the same sites and under similar conditions each time. Treat it as a field estimate rather than a lab-grade measurement.
Men: BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76 Women: BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387 All measurements in centimeters. Fat mass = weight × (BF% / 100) Lean mass = weight − fat mass
Result: Body Fat: 18.5% | Fat Mass: 15.2 kg | Lean Mass: 66.8 kg | Category: Fitness
For a male, 178 cm tall, 38 cm neck, 86 cm waist: BF% = 86.010 × log₁₀(86 − 38) − 70.041 × log₁₀(178) + 36.76 = 86.010 × 1.681 − 70.041 × 2.250 + 36.76 = 18.5%. At 82 kg, fat mass = 15.2 kg, lean mass = 66.8 kg, placing him in the "Fitness" range.
| Classification | Men | Women | |---|---|---| | Essential Fat | 2–5% | 10–13% | | Athletes | 6–13% | 14–20% | | Fitness | 14–17% | 21–24% | | Average | 18–24% | 25–31% | | Obese | 25%+ | 32%+ |
Consistency is key. Always measure at the same time of day, use the same tape (non-stretch), and measure to the nearest 0.5 cm. For the waist, breathe normally and measure at the end of a normal exhale — don't suck in. For the neck, measure at the narrowest point below the laryngeal prominence (Adam's apple). Take three readings and average them.
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This calculator applies the U.S. Navy circumference method by using sex-specific logarithmic equations that combine height with neck and waist measurements for men, and height with neck, waist, and hip measurements for women. It produces a practical field estimate of body fat percentage from tape measurements rather than from calipers or laboratory instruments.
The output is best used for repeated trend checks under the same measurement conditions. The method is useful because it is simple to repeat, but it remains a regression estimate rather than a direct measurement of body composition.
The Navy method typically estimates body fat within ±3-4% of DEXA results for most people. It's more accurate for individuals with average builds. It may overestimate body fat in muscular individuals (large waist from muscle, not fat) and underestimate in those with disproportionate fat distribution. For tracking changes over time, consistency in measurement technique matters more than absolute accuracy.
Neck circumference serves as a proxy for upper body lean mass. Subtracting it from waist circumference helps distinguish between someone who has a large waist due to muscle vs. fat. A thicker neck typically indicates more lean mass, which reduces the body fat estimate. This correction improves accuracy compared to using waist alone.
Women store more fat in the hip and gluteal region due to hormonal differences (estrogen promotes lower-body fat storage). Adding hip circumference to the formula captures this sex-specific fat distribution pattern. Men tend to store more fat abdominally, which the waist measurement already captures. The different formulas account for these biological differences.
It varies by sex and age. For men: essential fat 2-5%, athlete 6-13%, fitness 14-17%, average 18-24%, obese 25%+. For women: essential fat 10-13%, athlete 14-20%, fitness 21-24%, average 25-31%, obese 32%+. Women naturally carry more essential fat due to reproductive functions. Healthy ranges increase slightly with age.
Yes. The U.S. Department of Defense uses circumference-based body-fat screening for service members who exceed weight-for-height standards. Each branch (Army, Navy, Marines, Air Force) uses the same basic formula but may have different maximum allowable body fat percentages. It is a common field method rather than a lab measurement.
DEXA is a common reference method (±1-2% accuracy). Hydrostatic weighing is very accurate (±2%). Bioelectrical impedance (BIA) varies widely (±4-8%). Skinfold calipers depend on tester skill (±3-5%). The Navy method (±3-4%) is competitive with calipers and BIA, without requiring any equipment beyond a tape measure.