Body Fat % Calculator (Navy Method)
Estimate body fat percentage using the US Navy circumference method. Enter height, neck, waist (and hip for women) measurements in centimetres.
How to use this tool
- Enter sex, height, neck circumference, waist circumference, hip circumference (women) and body weight (optional) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your body fat % and the full breakdown beneath it.
The US Navy circumference method estimates body fat from simple tape measurements without calipers or DEXA. It is widely used in military fitness assessments.
This is an estimate only. DEXA scanning or hydrostatic weighing provide more accurate measurements. Not medical advice.
⚠ This tool is for general information and education only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Formula
Male: Body fat % = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Female: Body fat % = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
All measurements in centimetres.
How it works
The US Navy circumference method estimates body density from the circumferences of the waist, neck, and (for women) hips — sites that capture abdominal and gynoidal fat accumulation — then converts density to body fat percentage using the Siri equation. It does not require underwater weighing or DEXA scanning, making it practical for field use. Accuracy is typically ±3–4 percentage points versus DEXA; errors increase at extreme body compositions or if measurements are taken inconsistently.
Worked example
- Male: height = 175 cm, neck = 38 cm, waist = 85 cm.
- log₁₀(waist − neck) = log₁₀(47) ≈ 1.6721; log₁₀(175) ≈ 2.2430.
- Denominator = 1.0324 − 0.19077 × 1.6721 + 0.15456 × 2.2430 = 1.0324 − 0.3190 + 0.3467 = 1.0601.
- Body fat % = 495 ÷ 1.0601 − 450 ≈ 466.9 − 450 = 16.9%.
Body fat percentage = 16.9%.
Common mistakes to avoid
- Measuring waist circumference at the navel rather than at the narrowest point (women) or at navel height with a relaxed abdomen (men), producing inconsistent inputs.
- Taking a single measurement instead of averaging three consecutive readings — tape placement variation alone can shift body fat % by 2-3 points.
- Mixing measurement units — entering waist and neck in inches but height in centimetres, or vice versa, produces wildly incorrect results because the logarithmic formula requires consistent units throughout.
Key terms
- US Navy circumference method
- A body fat estimation technique developed for the US military that uses neck and waist (and hip for women) measurements in a logarithmic formula to predict body density.
- Body density
- Mass per unit volume of body tissue; fat tissue is less dense than lean tissue, so a lower density indicates a higher fat fraction.
- Siri equation
- The formula BF% = (495 ÷ body density) − 450, which converts body density to an estimated body fat percentage.
- Lean mass
- Everything in the body that is not fat: muscle, bone, organs, water, and connective tissue; calculated here as body weight × (1 − body fat fraction).
- DEXA (dual-energy X-ray absorptiometry)
- A clinical imaging method considered the reference standard for body composition measurement; the Navy method is validated against it but is less precise.
Frequently asked questions
- How accurate is the Navy method?
- Studies put the margin of error at ±3–4% compared with DEXA. It is less accurate for very lean or very obese individuals.
- Where do I measure the waist?
- For men: at the navel. For women: at the narrowest point. Keep the tape level and breathe normally — don't suck in.