Start with the error band
Historical evidence reports a standard measurement error of about 3.5 body-fat percentage points for these circumference equations, so the result is better understood as a range.
Body Fat Calculator (U.S. Navy Method)
Estimate body fat, fat mass, lean mass, and an approximate ±3.5-point error band from height and body circumferences. Calculations stay in your browser.
Calculate body fat
Live result
Complete all required fields to see the result.
Estimated body fat
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- Estimated fat mass
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- Estimated lean mass
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- Circumference combination
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- Reference category
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Common adult fitness reference ranges
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These ranges are not adjusted for age, ethnicity, or health status and only help place the estimate in context.
How to use
- Choose sex, units, and measurement countSelect metric or imperial units. Choose a three-measurement average to reduce random measurement variation.
- Enter circumferences at the specified locationsEnter height, weight, neck, and waist measurements. Women also enter hip measurements. Keep the tape level without compressing the skin.
- Review the estimate and error bandCompare the body fat estimate, approximate ±3.5-point error band, fat mass, lean mass, and non-diagnostic reference category.
Understanding the result
Best used for trends
Repeated measurements under consistent timing, placement, posture, and breathing conditions are more useful than comparing single results from different methods.
Not a health diagnosis
Body-fat percentage is only one part of body composition. It cannot determine health by itself or guide treatment or extreme diet and training decisions.
Scope and important limitations
- Tape position, breathing, and tape tension can materially affect the result. Averaging three measurements reduces only some random error.
- The approximate ±3.5 points reflects the historical equation's standard measurement error and is not a confidence interval for every individual.
- This tool implements the classic neck, waist, and hip equations. It must not be used to determine compliance with current U.S. Navy body-composition standards, which may use different procedures.
- Do not rely on this tool during pregnancy, for minors, marked edema, unusually high muscularity or body shape, or when measurement is restricted. It does not replace diagnosis or treatment advice.
Formula, examples, privacy, and sources
Formula and calculation assumptions
The tool converts all lengths to centimetres before using base-10 logarithms. Weight is not part of the body-fat percentage formula and is used only to calculate fat mass and lean mass.
Men: 495 ÷ [1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)] − 450
Women: 495 ÷ [1.29579 − 0.35004 × log10(waist + hips − neck) + 0.22100 × log10(height)] − 450
Use the same unit for every circumference. Men's waist must exceed neck circumference; women's waist plus hips must exceed neck circumference. Categories use the unrounded result, while displayed values use one decimal place.
Verified examples and unit consistency
Example for men
Height 175 cm, weight 75 kg, average neck 39 cm, and average waist 85 cm produce an estimated 16.2% body fat and about 12.1 kg fat mass.
Example for women
Height 165 cm, weight 60 kg, average neck 33 cm, average waist 75 cm, and average hips 95 cm produce an estimated 26.9% body fat and about 16.2 kg fat mass.
Divide lengths by 2.54 and multiply weight by 2.2046226218 for imperial input. The tool converts them back to centimetres and kilograms internally, so the underlying result is the same.
Privacy and local processing
The tool does not upload input, call third-party APIs, load CDNs or online fonts, or request camera, microphone, file-system, or location access.
Local storage keeps only unit and measurement-count preferences, not body measurements. Copying a share link adds the current input to the URL; sharing that link also shares those values.
Authoritative sources and licensing
- U.S. Navy Guide 4: Body Composition Assessment (2023)Reference for classic male neck/abdominal and female neck/natural-waist/hip measurement locations and combinations.
- MyNavyHR Guide 4: Body Composition Assessment (current public edition)Supports the notice that the current official BCA procedure has changed and that this tool must not determine service eligibility.
- National Academies / NCBI Bookshelf: Body Composition in the Military ServicesSupports the approximate 3.5-body-fat-point standard measurement error reported for the classic U.S. Navy circumference equations.
- American Council on Exercise: body-fat reference materialUsed for general adult fitness reference categories, not medical diagnosis.
The formulas and interface code are independently implemented. No third-party code, icons, images, or substantial passages are reproduced. External links provide factual citations and do not grant redistribution rights.
Frequently asked questions
Why do measurements taken on the same day produce different results?
Tape position and tension, breathing, and time of measurement all affect circumference. Measure three times under consistent conditions and focus on longer-term trends rather than a single decimal result.
Do centimetres and inches produce different body-fat results?
Not for the same physical measurements. The tool converts all lengths to centimetres before calculation; rounding values entered in the fields may cause very small display differences.
Can this result replace a medical exam or professional body-composition test?
No. Circumference methods are estimates and individual error may be substantial. Consult a physician, registered dietitian, or another qualified professional if you need greater accuracy or are concerned about the result.
Why is body weight required?
Weight is not part of the body-fat percentage equation. It is used to convert the estimated percentage into fat mass and lean mass.