Body Fat Calculator (U.S. Navy Method)
The U.S. Navy method estimates body fat percentage from a few circumference measurements with a tape measure. It is convenient and free, and reasonably accurate for most people, though it underestimates body fat for the very lean or very muscular.
Enter your sex, height, neck and waist (in centimetres), and hip if applicable. The calculator returns your estimated body fat percentage.
It is a good step up from BMI when you want to know how much of your weight is fat rather than muscle, without needing any equipment beyond a tape measure.
Enter your values to see the result.
How this is calculated
This calculator estimates body-fat percentage from circumference measurements using the U.S. Navy method. For men, it uses 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women, it uses 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450. All measurements are in centimetres.
The method is convenient and free, and is usually within about 3–4 percentage points of clinical methods for most adults. Because it relies on waist and neck (and hip for women), it captures abdominal fat, which BMI misses.
The formula takes a logarithm of (waist − neck), so the waist must exceed the neck for men, and (waist + hip) must exceed the neck for women — otherwise the maths breaks and the calculator returns no result. The estimate is less reliable for the very lean or very muscular, where calipers, hydrostatic weighing or DEXA are more accurate. Measurement error is the biggest practical issue: measure flat, at the right landmarks, after a normal exhale, and average two readings.
Worked example
A man, 175 cm tall, neck 38 cm, waist 85 cm.
- 1log10(waist − neck) = log10(85 − 38) = log10(47) ≈ 1.672.
- 2log10(height) = log10(175) ≈ 2.243.
- 3Denominator = 1.0324 − 0.19077 × 1.672 + 0.15456 × 2.243 ≈ 1.060.
- 4Body fat = 495 ÷ 1.060 − 450 ≈ 17.0%.
Frequently asked questions
- How accurate is the Navy method?
- It is usually within about 3–4 percentage points of clinical methods for most adults. It is less reliable for very muscular or very lean individuals, where calipers or DEXA are better.
- Where do I measure neck and waist?
- Neck: below the larynx, measured flat. Waist: at the navel for men, at the narrowest point for women. Keep the tape horizontal and snug but not compressing the skin.
- Why must waist exceed neck?
- The formula takes the logarithm of (waist − neck), so the waist measurement must be larger than the neck for the maths to work. If it is not, re-measure — the values may be swapped.
- How accurate is the Navy method?
- It is usually within about 3–4 percentage points of clinical methods for most adults. It is less reliable for very muscular or very lean individuals, where calipers or DEXA are better.
- Where do I measure neck and waist?
- Neck: below the larynx, measured flat. Waist: at the navel for men, at the narrowest point for women. Keep the tape horizontal and snug but not compressing the skin, and measure after a normal exhale.
Related calculators
Method: U.S. Navy circumference body-fat equations. No external data source. Last updated: September 2026.
These results are general estimates from established formulas and are not medical advice. They depend on the accuracy of the values you enter and on individual factors the formulas cannot capture. Consult a qualified healthcare professional before making decisions about your diet, training or treatment.