Body Fat Calculator
Estimate body fat percentage using the US Navy circumference method. Also calculates BMI, lean body mass, and body fat category with color-coded interpretation.
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Disclaimer: For educational purposes only. The Navy method is an estimate — DEXA or hydrostatic weighing are more precise. Not a substitute for clinical judgment.
About This Tool
What Is Body Fat Percentage?
Body fat percentage is the proportion of your total body weight that is composed of fat tissue. Unlike BMI, which uses only height and weight, body fat percentage differentiates between fat mass and lean mass (muscle, bone, organs, water). This makes it a more meaningful metric for assessing fitness, health risk, and body composition changes over time. Essential body fat is necessary for normal physiological function — it insulates organs, regulates hormones, and stores energy. Women require higher essential fat (10–13%) than men (2–5%) due to reproductive physiology.
How the US Navy Body Fat Method Works
The US Navy method (Hodgdon-Beckett equations) estimates body fat percentage from simple circumference measurements: height, neck, waist, and hip (women only). It was developed by the Naval Health Research Center in 1984 as a practical field method requiring only a tape measure. The DoD uses it for military fitness standards. The formulas use logarithmic relationships between circumference ratios and body density, then convert to body fat percentage. Accuracy is typically within ±3–4% of DEXA (dual-energy X-ray absorptiometry), which is considered the gold standard.
How to Calculate Body Fat Percentage
For men: %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. For women: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. All measurements must be in centimeters. The calculator performs unit conversions automatically if you enter measurements in inches. A larger waist relative to neck (and height) indicates higher body fat. The hip measurement for women accounts for sex-specific fat distribution patterns.
Body Fat vs. BMI
BMI (Body Mass Index = weight/height²) is a simple screening tool but has well-known limitations. It classifies muscular individuals as "overweight" and may miss "normal-weight obesity" — people with healthy BMI but excess body fat. Body fat percentage provides a more direct measure of adiposity. That said, BMI remains useful for population-level studies and initial screening. For individual assessment, especially in athletes or those with significant muscle mass, body fat percentage is more informative.
🔑 Clinical Pearls
- The Navy method is least accurate at the extremes — very lean (athletes) or very obese individuals. DEXA or hydrostatic weighing is preferred when precision matters.
- Waist circumference alone is a strong predictor of cardiometabolic risk: >40 inches (102 cm) for men and >35 inches (88 cm) for women indicates elevated risk regardless of body fat percentage.
- Body fat percentage increases with age even when weight remains stable, due to sarcopenia (loss of muscle mass). Resistance training helps preserve lean mass.
- "Normal-weight obesity" (normal BMI, high body fat %) is associated with metabolic syndrome, increased cardiovascular risk, and higher mortality — body fat % helps identify this phenotype.
- Body fat categories are general guidelines. Optimal body fat depends on individual factors including age, sex, fitness goals, and overall health status.
Key References
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center. Report No. 84-29. 1984.
- Gallagher D, et al. Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. Am J Clin Nutr. 2000;72(3):694–701.
- Romero-Corral A, et al. Accuracy of body mass index in diagnosing obesity in the adult general population. Int J Obes. 2008;32(6):959–966.
Formula last verified: February 2026