Body Fat Calculator (U.S. Navy Method)
Measure your neck and waist (women also the hips) with a tape measure and enter your height. The calculator estimates your body fat percentage with the U.S. Navy circumference method.
How it is calculated
How the U.S. Navy method works
The formulas come from two reports by the Naval Health Research Center (Hodgdon and Beckett, 1984). Body density is first estimated from height and circumferences, all in centimetres:
- Men: density = 1.0324 − 0.19077 × log₁₀(abdomen − neck) + 0.15456 × log₁₀(height)
- Women: density = 1.29579 − 0.35004 × log₁₀(waist + hips − neck) + 0.22100 × log₁₀(height)
Density is then converted to fat percentage with Siri's equation (1961): body fat % = 495 ÷ density − 450. Inch values are converted to centimetres exactly first (1 in = 2.54 cm).
Example (man): 70 in tall (177.8 cm), neck 15 in (38.1 cm), abdomen 33.5 in (85.09 cm). Abdomen − neck = 46.99 cm, log₁₀ = 1.6720; log₁₀(177.8) = 2.2499. Density = 1.0324 − 0.19077 × 1.6720 + 0.15456 × 2.2499 = 1.0612. Body fat = 495 ÷ 1.0612 − 450 ≈ 16.5%.
How to measure
- Neck: just below the larynx, tape sloping slightly downward at the front.
- Abdomen (men): horizontally at the level of the navel, after a normal breath out.
- Waist (women): at the narrowest point, roughly midway between the lower tip of the breastbone and the navel.
- Hips (women): at the widest point of the buttocks.
Keep the tape snug without compressing the skin. Measuring twice and averaging reduces errors.
How accurate is it?
The equations were checked against underwater weighing in Navy personnel. The standard error of estimate was 3.5 percentage points for men (2.7 in a cross-validation with 100 other men) and 3.7 for women (4.0 to 4.4 in cross-validation). A result of 16% may therefore easily lie between about 12.5% and 19.5%. The calculator shows this range as well.
The calculator deliberately gives no rating such as "good" or "too high": the reports only mention the Navy's service limits of the time, not medical cut-offs. The result is an estimate, not a diagnosis, and does not replace medical advice.
Frequently asked questions
How accurate is the U.S. Navy method?
In the original reports the standard error of estimate against underwater weighing was about 3.5 percentage points for men and 3.7 for women. That is fine for a rough estimate and for tracking change over time, but not for a precise measurement.
Why do women need a hip measurement?
For women, the combination of waist, hips and neck predicted body density best; for men, abdomen and neck are enough. The two equations were developed separately in 1984.
Where exactly do I measure my waist?
Men measure horizontally at the navel, women at the narrowest point of the waist. Ideally measure in the morning, after a normal breath out and without pulling the stomach in.
Can I compare the result with a body fat scale?
Only to a limited extent. Bioelectrical impedance scales measure differently and react to hydration, for example. Compare values within the same method.
What body fat percentage is normal?
The calculator does not give a rating because the underlying reports do not set medical cut-offs. Discuss how to interpret your value with your doctor.
Sources and legal basis
- DTIC ADA143890: Hodgdon J. A., Beckett M. B.: Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, Report 84-11, 1984
- DTIC ADA146456: Hodgdon J. A., Beckett M. B.: Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center, Report 84-29, 1984
As of:
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