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Navy Body Fat Calculator

Estimate your body fat with the Navy method.

How it is calculated

All lengths are in centimetres and weight in kilograms. For men the formula is BF% = 495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450. For women it is BF% = 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450, so hip is required and ignored for men.

If weight is given, fat mass = weight × BF% ÷ 100 and lean mass = weight − fat mass; without weight both are shown as a dash. A result below zero is shown as 0. The measurement inside the logarithm must be positive (for men, waist must be larger than neck), otherwise nothing is returned. It is an estimate from tape measurements, so it is less precise than a body scan.

Worked example

A man 178 cm tall, neck 38 cm, waist 90 cm, weighing 80 kg.

Waist − neck = 52, log₁₀(52) ≈ 1.7160 and log₁₀(178) ≈ 2.2504. The denominator is 1.0324 − 0.19077 × 1.7160 + 0.15456 × 2.2504 ≈ 1.0529. Then 495 ÷ 1.0529 − 450 ≈ 20.15%. Fat mass = 80 × 0.2015 ≈ 16.12 kg and lean mass = 80 − 16.12 = 63.88 kg.

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Common mistakes

  • Entering height and tape measurements in inches or feet. The formula in this tool uses centimetres, and inch values give a meaningless percentage.
  • Measuring the waist at a different place each time. Keep the same position and posture for every measurement; the log formula magnifies small differences.
  • Leaving the sex field on the default (male) when calculating for a woman, or leaving out the hip for women. Female results need the hip circumference.
  • Pulling the tape tight enough to compress the skin. A 1 cm error in neck or waist changes the percentage noticeably (for this man, a waist of 91 cm instead of 90 cm raises it by about 0.7 points).
  • Expecting weight to change the percentage. It only splits the result into fat and lean kilograms.

Sources

About this calculator

This calculator applies the US Navy circumference method (developed by Hodgdon and Beckett in 1984), which estimates body fat percentage from simple tape measurements rather than calipers or a DEXA scan. For men it uses neck and waist circumference plus height in a log₁₀-based formula; for women it adds hip circumference, since fat distribution patterns differ by sex. Enter measurements in centimeters. If you also enter your weight in kilograms, the result breaks down into fat mass and lean (fat-free) mass in kilograms.

The US military uses this exact method for body-composition fitness standards and readiness assessments, and it has become popular well beyond the armed forces because it needs only a measuring tape — personal trainers and fitness enthusiasts use it to track body composition changes over time without access to more expensive equipment like skinfold calipers or hydrostatic weighing.

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  • Editorial team

    Because the formula takes logarithms of tape differences, small measuring slips matter more than they look. For a man with height 175, neck 38 and weight 80, a waist of 85 cm gives 16.94 percent and 86 cm gives 17.71, so a single centimetre moves it by about 0.8 points. Measure the waist three times at the same spot after a normal exhale and use the middle value. If you have a scan result to compare with, tell us how far apart they were.

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