Body Fat Calculator Direct Overview
Estimate body fat percentage using the US Navy Circumference Method. Widely used for its simplicity and reasonable accuracy compared to clinical standards. Requires waist and neck for men, and waist, hip, and neck for women.
Body Composition Index
Body Fat Calculator
Estimate body fat percentage using the US Navy Circumference Method. Widely used for its simplicity and reasonable accuracy compared to clinical standards. Requires waist and neck for men, and waist, hip, and neck for women.
System Units
Awaiting Calculator Inputs
Fill in the fields above and hit Calculate to generate your body composition targets.
Formula & Math
Uses sex-specific logarithmic equations based on circumference measurements relative to height.
How to Interpret
Body fat estimates represent body composition categories (essential, athletic, fit, average, excess). Track changes in measurements over time.
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 BodyCompOS Review Board
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.
Related Strategy Tools
Body Composition Calculator
Calculate your lean body mass, fat mass, fat-free share, and body composition proportions using your body weight and body fat percentage. Provides a complete compartmentalized snapshot of your physical structure.
Lean Body Mass Calculator
Calculate Lean Body Mass (LBM) from body weight and body fat percentage. LBM = Weight × (1 - BF/100). Differentiates metabolic tissue from stored fat for body composition assessment, calorie targeting, and goal planning.
FFMI Calculator
Calculate Fat-Free Mass Index (FFMI) to quantify muscle mass relative to height. Uses raw FFMI with Kouri height normalization to correct tall-athlete skew. Provides body composition context beyond BMI for training and strategy planning.