Body Fat Calculator

Estimate body fat percentage from simple tape measurements using the U.S. Navy method.

How the Math Works

The U.S. Navy method calculates body fat percentage using logarithmic measurements of key body circumferences combined with height. For men, it employs the formula: 86.01 × log₁₀(waist - neck) - 70.041 × log₁₀(height) + 36.73, while women use: 163.205 × log₁₀(waist + hip) - 97.684 × log₁₀(height) - 78.387. These equations weight circumference ratios relative to height, leveraging the relationship between body shape and fat distribution to estimate total body fat. The logarithmic transformation accounts for non-linear scaling between measurements and actual fat mass.

Practical Applications

To use this calculator, first measure your waist (at the navel for men, at the narrowest point for women), neck circumference (just below the larynx), and hip (at the widest point for women). For accuracy, ensure measurements are taken in a relaxed state with a snug but non-compressive tape. Input these values along with your height into the calculator, which applies the logarithmic formulas to generate your body fat percentage. This method is particularly useful for athletes or individuals tracking fitness progress, as it provides a more nuanced assessment than BMI by considering body composition rather than just weight-to-height ratios.

Day-to-Day Use

Knowing your body fat percentage helps set realistic fitness goals and monitor dietary or exercise changes, such as tracking progress during a cutting phase or assessing muscle gain. Unlike BMI, it differentiates between fat and lean mass, offering clearer insights into health risks associated with excess visceral fat. Whether managing weight, optimizing athletic performance, or simply understanding body composition, this tool provides actionable data to guide lifestyle choices like meal planning, strength training, or cardiovascular routines. Regular tracking can also boost motivation by visually demonstrating incremental improvements in fitness over time.

Worked example

Male, 70 in tall, 34 in waist, 15 in neck → about 17% body fat.

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