US Navy method, in seconds.
Disclaimer: this tool is for informational purposes only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Estimate body fat percentage from neck, waist, and (women) hip measurements.
Estimate body fat percentage from neck, waist, and (women) hip measurements.
Uses the US Navy circumference formula based on log-ratios of body measurements.
Male, 175 cm, neck 38, waist 85 → ≈ 18% body fat.
Body fat percentage tells you what your weight is actually made of. Two people at the same BMI can have radically different body fat — and radically different health risks. Tracking %BF gives you a much more useful picture of fitness and health than the scale ever can.
The American Council on Exercise (ACE) publishes widely cited body fat guidelines. For men: essential 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, obese 25%+. For women: essential 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, obese 32%+. Women carry more essential fat for hormonal and reproductive health. Age also shifts these ranges upward by 1–3% per decade after 30.
DEXA scans are the gold standard but cost $50–150 and require a clinic visit. Bioelectrical impedance (BIA) scales are convenient but vary 3–8% based on hydration. The US Navy circumference method, used in this calculator, requires only a tape measure and produces results within 3–4% of DEXA for most adults. Skinfold calipers in trained hands are also highly accurate. For tracking changes over months, consistency of method matters more than absolute precision.
The fastest way to ruin a body recomposition is to crash diet without strength training. Aim for a moderate calorie deficit (300–500 kcal/day), eat 0.7–1.0 g of protein per pound of body weight, and lift weights 3–4× per week. Studies in the American Journal of Clinical Nutrition show that this combination preserves nearly all lean mass during fat loss, while pure cardio + low calories typically loses 25%+ of weight from muscle.
ACE classifies 14–24% as healthy for men and 21–31% for women. Athletes typically sit lower (6–13% men, 14–20% women), but going below essential fat (2% men, 10% women) carries serious hormonal and immune risks. Aim for the 'fitness' or 'average' band for long-term health.
The US Navy method is one of the most accurate field methods available. Validation studies put it within 3–4% of DEXA scans for most adults — close enough to track real progress at home with just a tape measure. It is less reliable for very lean athletes or people with extreme body shapes.
Yes — this is called body recomposition. By eating slightly under maintenance with high protein and consistent strength training, beginners and returning lifters can build muscle and lose fat simultaneously. The scale may not move much, but body fat % drops and physique visibly improves.
For informational purposes only. Consult a certified medical professional before making health decisions.
Men: %BF = 495 / (1.0324 − 0.19077·log10(waist−neck) + 0.15456·log10(height)) − 450
We use the US Navy circumference method, originally developed by the Naval Health Research Center. It uses neck, waist, and (for women) hip measurements alongside height to estimate body fat percentage. It typically falls within 3–4% of DEXA scan results for most adults — accurate enough for tracking trends, not a clinical diagnosis.
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