Body Fat Percentage Calculator
Estimate body fat percentage using the US Navy circumference method (waist, neck, and for women hip measurements). Use it as a no-equipment-needed alternative to skinfold calipers, BIA, or DEXA for tracking body composition trends.
Last updated: May 2026
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About this calculator
The formula uses the US Navy method (Hodgdon-Beckett, 1984), originally developed for military fitness assessments. Male formula: BF% = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. Female formula: BF% = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450. All measurements in cm. The method estimates body fat from circumferences at fat-storage sites (waist for both sexes, plus hip for women) compared to lean reference sites (neck, height). Accuracy: typically ±3-4% vs DEXA gold standard for average body types; less accurate for very lean or muscular individuals (where the formula may underestimate body fat) and very obese individuals (where it may overestimate). For consistent tracking, measure consistently: same time of day (typically morning), same hydration state, in identical body posture, with measuring tape held parallel to floor and snug but not compressing skin. Measurement sites: waist measured at narrowest point (typically at navel level for men, above hips for women); neck measured below larynx (Adam's apple); hip measured at widest point for women. Healthy body fat ranges: men athletic 6-13%, fitness 14-17%, average 18-24%, obese 25%+; women athletic 14-20%, fitness 21-24%, average 25-31%, obese 32%+. Essential fat (minimum for survival): men ~3-5%, women ~10-13%. Below essential fat, hormonal and immune function suffer; this is rare except in elite physique-sport competitors during contest prep. Edge cases: measurements that produce calculated body fat below 3% (men) or 10% (women) indicate measurement error rather than actual very-low body fat; recheck technique. The formula doesn't handle very tall, very short, or atypical body shapes well.
How to use
Example 1 — Average male. Male, 180 cm height, 90 cm waist, 40 cm neck. Computing the male formula: log10(90 − 40) = log10(50) = 1.699; log10(180) = 2.255. BF% = 495 / (1.0324 − 0.19077 × 1.699 + 0.15456 × 2.255) − 450 = 495 / (1.0324 − 0.324 + 0.349) − 450 = 495 / 1.057 − 450 = 468.3 − 450 = 18.3%. ✓ This falls in the "average" male range (18-24%). A reasonable estimate for a typical adult male with desk job and moderate activity. Example 2 — Female. Female, 165 cm height, 75 cm waist, 100 cm hip, 33 cm neck. Female formula: log10(75 + 100 − 33) = log10(142) = 2.152; log10(165) = 2.217. BF% = 495 / (1.29579 − 0.35004 × 2.152 + 0.22100 × 2.217) − 450 = 495 / (1.29579 − 0.753 + 0.490) − 450 = 495 / 1.033 − 450 = 479.2 − 450 = 29.2%. ✓ Falls in average female range (25-31%). Consistent with a typical adult woman; weight management or fitness training could push this lower over months.
Frequently asked questions
How accurate is the Navy body fat method?
Typically within ±3-4% of lab-measured (DEXA) body fat for average body types. Better for adults with typical body proportions; less accurate for very lean athletes (often underestimates true BF by 2-5%), very muscular individuals (may underestimate), and obese individuals (may overestimate). For comparison: skinfold calipers in experienced hands ±2-3%; bioelectrical impedance (smart scales) ±5-8%; DEXA scan ±1-2%; underwater weighing ±2-3%. The Navy method has the advantage of requiring only a tape measure and being free; calipers cost $20-50, BIA scales $50-200, DEXA scans $50-150 per scan. For tracking trends over time, the Navy method is excellent because measurement error is consistent within an individual — if your circumference numbers reduce by 5 cm at waist, your real body fat has dropped meaningfully even if the absolute calculated percentage is slightly off.
What are healthy body fat percentages?
American Council on Exercise (ACE) standards by body fat percentage: Men — Essential fat 2-5%, Athletes 6-13%, Fitness 14-17%, Average 18-24%, Obese 25%+. Women (higher because of essential fat for hormonal function) — Essential fat 10-13%, Athletes 14-20%, Fitness 21-24%, Average 25-31%, Obese 32%+. Below essential fat percentages, hormonal disruption (especially in women, can cause amenorrhea and bone density loss), immune dysfunction, and difficulty maintaining body temperature occur. Above the "obese" thresholds, metabolic syndrome risk, cardiovascular disease risk, and type 2 diabetes risk all rise significantly. The "fitness" range (14-17% men, 21-24% women) is widely considered the sweet spot for athletic performance and aesthetic muscle definition without compromising hormonal function. Body fat distribution also matters: visceral fat (around organs) is more metabolically harmful than subcutaneous fat (under skin); waist-to-hip ratio and waist circumference assess this independently of total body fat percentage.
How do I measure correctly?
Take measurements: in the morning, before eating or drinking large amounts; after bathroom; consistent hydration state; in front of a mirror so you can see proper tape positioning; bare skin or with light clothing only. Waist (men): narrowest point, typically at navel level. Waist (women): above hips at narrowest point, typically about an inch above navel. Neck: below the larynx (Adam's apple for men, equivalent area for women), with tape angled slightly downward from front to back. Hip (women only): widest point of the hips, typically at the largest part of the buttocks. Tape should be: snug against skin but not compressing; parallel to the floor; not twisted. Take 2-3 measurements at each site and average. For tracking: measure once per week or every 2 weeks, same conditions, same time of day. For meaningful tracking, log measurements separately (each site) rather than just calculated body fat — site-specific changes are often visible even when calculated % is stable.
What are the most common mistakes people make with body fat measurement?
The biggest is inconsistent measurement technique — different tape positioning, posture, or hydration state produces calculated body fat changes of 1-3% with no real change. The second is using consumer BIA smart scales without understanding their ±5-8% error; daily fluctuations of 1-2% are often noise, not real change. The third is obsessing over absolute body fat percentage when tracking trends is more meaningful — most calculation methods are precise (consistent within themselves) but not perfectly accurate (matching DEXA exactly). The fourth is comparing body fat across calculation methods (Navy vs BIA vs caliper) and treating any disagreement as one being "wrong"; all have systematic biases vs DEXA, and the right approach is picking one method and tracking with it consistently. The fifth is focusing on body fat percentage when waist circumference and waist-to-height ratio are better predictors of cardiovascular risk. The sixth is using crash diets to lower body fat aggressively; rapid loss includes muscle loss which permanently lowers metabolism — slow, sustainable fat loss (0.5-1% body fat per month) preserves muscle.
When should I not use this calculator?
Skip it for very lean athletes (under 10% BF for men, under 18% for women) where the formula underestimates body fat by 2-5%; use skinfold calipers or DEXA for those situations. It is the wrong tool for very tall (over 200 cm) or very short (under 150 cm) individuals where the formula's height assumptions break down. Do not use it for medical body composition assessment (cancer treatment, eating disorder recovery, bariatric surgery); use DEXA or BIA in a clinical setting. For young athletes (under 18), body fat standards differ from adult populations; use age-appropriate references. For pregnant or recently postpartum women, the formula doesn't apply due to dramatic body composition changes. For competitive bodybuilders or physique athletes at contest weight, use DEXA or specialized methods (BodPod, hydrostatic) for precise tracking. And for general weight management, focus on waist circumference (changes meaningfully with fat loss) and consistent exercise rather than chasing precise body fat percentages.