Estimate body fat percentage, lean muscle mass, and fat mass using the clinically proven U.S. Navy circumference method.
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A body fat percentage calculator estimates the proportion of your total body weight composed of adipose fat tissue versus lean tissue (muscle, bones, water, and organs). Utilizing the standardized U.S. Navy circumference equations (Hodgdon & Beckett), this tool provides a far more accurate assessment of health and physical fitness than BMI alone.
\% \text{BF} = \frac{495}{\text{Body Density}} - 450Men Body Density = 1.0324 - 0.19077 × log10(waist - neck) + 0.15456 × log10(height). Women Body Density = 1.29579 - 0.35004 × log10(waist + hip - neck) + 0.22100 × log10(height).
Scenario: A 32-year-old male measuring 70 inches (178 cm), weighing 175 lbs (79.4 kg), with a 15.5-inch neck and 34-inch waist.
Waist minus neck: 34 - 15.5 = 18.5 inches (47.0 cm).
Calculate metric body density using Hodgdon & Beckett constants.
Apply Siri equation: (495 ÷ 1.0612) - 450 ≈ 16.4% body fat.
Fat mass: 175 lbs × 16.4% = 28.7 lbs. Lean mass: 175 - 28.7 = 146.3 lbs.
According to the American Council on Exercise (ACE): For men, 10–20% is considered healthy/fitness (6–13% for athletes). For women, 18–28% is healthy/fitness (14–20% for athletes). Women naturally carry higher essential fat for hormonal and reproductive health.
Studies demonstrate that the U.S. Navy circumference method is accurate within 3–4% of gold-standard DEXA scans and hydrostatic weighing, making it the most reliable tape-measure method available.
BMI only considers total weight relative to height and cannot differentiate between dense muscle mass and adipose fat. Muscular athletes are frequently misclassified as "overweight" by BMI, whereas body fat percentage evaluates true tissue composition.
Because healthy fat loss occurs at approximately 0.5% to 1.0% body fat every two to four weeks, measuring once every 2 to 4 weeks is optimal for tracking meaningful body recomposition.
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Ideal Range: 10% - 20%