Estimate your body-fat percentage with the U.S. Navy circumference method.
Estimated body fat
The U.S. Navy method estimates body density from your height and the circumference of your neck and waist (plus hips for women), then converts it to a body-fat percentage.
It is a quick, equipment-free estimate with a standard error of about 3.5%. It is not a substitute for DEXA or hydrostatic weighing.
It typically lands within 3–4% of hydrostatic weighing for most adults, but accuracy drops at the extremes of body composition.
Neck just below the larynx, waist at the navel (men) or the narrowest point (women), and hips at the widest point (women).
Fitness ranges are roughly 14–17% for men and 21–24% for women; essential fat is 2–5% and 10–13% respectively.
This calculator estimates your body-fat percentage using the U.S. Navy circumference method — a tape-measure approach that requires only your height, neck, waist, and (for women) hip measurements. The result places you in a standard fitness category and is a useful reference point for tracking body composition over time.
The headline figure is your estimated body-fat percentage. Because this is a circumference-based estimate, measurement accuracy has a direct effect on the result — even a centimetre off on the waist can shift the percentage by a point or two. Take each measurement at the same landmark each time for consistent tracking. The fitness category (Essential, Athlete, Fitness, Average, or Obese) is based on widely cited ACE body-fat norms.
A man 178 cm tall with a 40 cm neck circumference and a 90 cm waist circumference.
The estimated body-fat percentage is 18.7%, which falls in the Average category for men. No currency or monetary figures are involved; the inputs are body measurements in centimetres.
Research suggests this method estimates body fat within roughly 3–4 percentage points of hydrostatic (underwater) weighing for most healthy adults. Accuracy can be lower at very high or very low body-fat levels, or if measurement technique is inconsistent. It is an informational estimate, not a clinical measurement.
Body fat in women is more often distributed around the hips and thighs. Adding hip circumference to the formula captures that pattern and makes the estimate more representative of typical female body composition.
Measure the waist at the narrowest point (for men) or at the level of the navel (for women). Measure the neck just below the larynx (Adam's apple). Keep the tape snug but not compressing the skin, and record measurements in the morning for consistency.
The categories — Essential, Athlete, Fitness, Average, and Obese — are based on ACE (American Council on Exercise) body-fat norms. They are reference ranges, not medical diagnoses. A healthcare professional can put any result in proper context for your individual health situation.
No. This tool provides an informational estimate only. Methods such as DEXA scanning or hydrostatic weighing give more precise measurements. Always consult a qualified health professional before making decisions about diet, exercise, or body composition.
The calculator uses the U.S. Navy circumference method, published by Hodgdon and Beckett (1984) and widely cited in exercise science. The method first estimates body density from height and circumference measurements using a log-based regression formula: for men, density = 1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height); for women, density = 1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height). All measurements are in centimetres. Body-fat percentage is then derived from density using the Siri equation: %BF = 495 / density − 450. The result is rounded to one decimal place.
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