Body Composition Index
Body Fat Calculator
Estimate body fat percentage using the US Navy Circumference Method. Uses neck, waist, and hip measurements with sex-specific logarithmic formulas. Outputs body fat percentage, lean mass, and fat mass for body composition assessment and strategy selection.
System Units
Awaiting Calculator Inputs
Fill in the fields above and hit Calculate to generate your body composition targets.
Formula & Math
Combines entered body fat context with BMI and waist-to-height screening signals when available.
How to Interpret
Body fat estimates are noisy. Use consistent measurement methods and trend direction.
Plan Integration
Take these estimations back to the main Strategy Finder assessment, or save them in your tracking logs in the local dashboard.
Body Fat Percentage: Navy Circumference Model
Science & physiological analysis for strategy selection
Reviewed by Divy Yadav, CSCS
Last updated: June 27, 2026 · BodyCompOS Editorial Board
Understanding your body fat percentage is essential for selecting your primary body composition strategy. High body fat percentages indicate a caloric deficit (cutting) is appropriate, while lean baselines indicate a caloric surplus (lean bulking) or body recomposition is optimal. The BodyCompOS Body Fat Calculator uses the US Navy Circumference Method, developed by Hodgdon and Beckett at the Naval Health Research Center. It utilizes sex-specific logarithmic regression formulas incorporating waist, neck, and hip measurements to produce a reliable, low-cost composition estimate.
1. How to Use & Apply This Target
Take measurements in the morning before eating. Men should measure waist circumference at the navel and neck circumference below the larynx. Women should measure waist at the narrowest point, neck below the larynx, and hips at the widest point. Input these values to get your estimated body fat percentage. Use this value to guide your strategy choices and configure your calorie/protein calculators.
2. Mathematical Assumptions & Formula Logic
This calculator uses the official US Navy regression formulas. Height and circumference measurements are converted to inches. The male formula is: `86.010 * log10(Waist - Neck) - 70.041 * log10(Height) + 36.76`. The female formula is: `163.205 * log10(Waist + Hip - Neck) - 97.684 * log10(Height) - 78.387`. Measurements must be taken horizontally with a flexible tape, avoiding skin compression.
3. Step-by-Step Worked Mathematical Example
Frequently Asked Questions
Q:How accurate is the US Navy body fat method?
When compared to laboratory standard methods like DEXA or hydrostatic weighing, the US Navy method typically has a standard error of estimation of ±3% to 4%. For tracking progress, the absolute accuracy matters less than the relative consistency of measurement over time.
Q:Why does my waist size change daily?
Waist measurements can fluctuate by 1-2 cm due to digestive bloat, sodium intake, hydration levels, and glycogen storage. To ensure reliable trends, measure yourself first thing in the morning, after using the restroom, and calculate a weekly average.
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