Body Fat Calculator

How to take accurate measurements for the Navy formula

The US Navy body fat formula is only as accurate as the measurements you take. Measurement technique is standardized and must be followed consistently to get repeatable results.

Neck circumference: measure at the narrowest point of the neck, typically just below the larynx (Adam's apple). The tape should be level all the way around — not tilted. Stand up straight with your head in a neutral position. This measurement is typically 35–45 cm for men.

Waist circumference: measure horizontally around the abdomen at the navel level — not at the narrowest point of the torso (which is a different measurement used for the waist-to-hip ratio). The tape should be snug but not compressing the skin. Measure at the end of a normal exhale. This is the most variable measurement depending on time of day and food intake.

Hip circumference (women only): measure at the widest point of the hips and buttocks, with the tape horizontal all the way around. Stand with feet together. This is typically at the level of the greater trochanters.

For consistency: always measure at the same time of day (morning before eating is most reliable), use a non-stretchable measuring tape, take three measurements and use the average, and have someone else take your measurements if possible for more reliable positioning.

Body fat methods compared — tape vs caliper vs DEXA vs bioelectrical

Multiple methods exist for measuring body fat, each with different accuracy, cost, and accessibility.

Tape measure (Navy method): free, requires only a measuring tape, ±3–4% accuracy compared to DEXA. Suitable for tracking trends over time and is the method used by this tool.

Skinfold calipers: inexpensive ($10–50), measures subcutaneous fat thickness at multiple sites (typically 3, 7, or 9 sites), ±3–4% accuracy when done correctly by an experienced measurer. Requires practice and is difficult to self-administer on all sites.

Bioelectrical impedance (BIA): scales and handheld devices that pass a low electrical current through the body. Fast and convenient, but ±4–8% accuracy, highly influenced by hydration status. Dehydration (common after exercise or in the morning) significantly understates body fat. Consumer BIA scales are inexpensive but the most variable.

DXA (Dual-energy X-ray absorptiometry): the gold standard for body composition, typically ±1–2% accuracy. Measures bone mineral density, lean mass, and fat mass in different body regions. Available at medical facilities, universities, and some gyms for $50–150 per scan.

Hydrostatic weighing (underwater weighing): historically the gold standard (±1.5–2%), now mostly supplanted by DEXA in research settings.

Body fat and health — what the research shows

Body fat percentage matters not just as a total number, but where that fat is stored. Visceral fat — fat stored around internal organs in the abdominal cavity — is metabolically active and associated with elevated inflammatory markers, insulin resistance, type 2 diabetes, cardiovascular disease, and other metabolic conditions. Subcutaneous fat — fat stored just beneath the skin — is metabolically less active and carries lower health risk.

The waist circumference cutoffs used by the National Institutes of Health and the WHO to flag metabolic risk are: greater than 40 inches (102 cm) for men and greater than 35 inches (88 cm) for women. These thresholds are associated with significantly elevated risk of metabolic syndrome regardless of BMI category — some people with normal BMI but central obesity carry higher cardiometabolic risk than some overweight people without central fat accumulation.

Exercise, particularly resistance training combined with cardiovascular exercise, preferentially reduces visceral fat. Even moderate body weight loss (5–10% of body weight) reduces visceral fat significantly and produces measurable improvements in insulin sensitivity, blood pressure, and lipid profiles, typically before any visible external change in appearance.