Body composition calculator

Estimates body fat percentage from circumferences, calculates fat and lean mass and body mass index.

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Result

Body fat: 16.9%
Fat mass: 12.7kg
Lean mass: 62.3kg
Body mass index: 24.5kg/m²

Units: body fat in %, mass in kg, BMI in kg/m². Method source: the U.S. Navy formula (1984); body fat categories from ACE references, BMI categories from WHO.

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How it is calculated

Body fat is estimated with the U.S. Navy method (Hodgdon and Beckett, 1984): it uses height and the circumferences of neck and waist, plus hips for women. The method was chosen because it needs no equipment and its error is comparable to consumer bioimpedance scales. BMI is calculated as well using the WHO classification — it says nothing about composition but allows comparison with population norms.

Formula

Men: %fat = 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450; Women: %fat = 495 / (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.221 × log₁₀(height)) − 450; BMI = weight / height²

Limits of the method

The error is around ±3–4% against DXA and grows with atypical body shapes. Measure in the morning before eating, with the tape snug but not tight, at the same landmarks each time: a 1 cm difference at the waist noticeably shifts the result. BMI does not distinguish muscle from fat and does not apply to athletes, pregnancy or children.

Sources of the method

This calculation is for reference only and is not medical advice, a diagnosis or a prescription. If you have a medical condition, are pregnant, take medication or have any doubts, discuss the result with a physician or a qualified nutrition professional.

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What next

Formula breakdowns, biomarker reference ranges and nutrition articles with cited sources are in the NutriFit knowledge base.

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Calculation