Body Fat Percentage Calculator
Estimate your body fat percentage using the U.S. Navy tape measure method.
Updated April 2026 · CalcFlow Editorial
What is a Body Fat Percentage? A body fat percentage calculator estimates the proportion of your total body mass that is fat tissue. The U.S. Navy tape measure method uses waist, neck, and hip circumferences to estimate body density, then applies the Siri equation (Body Fat % = (495 / Body Density) - 450) to derive fat percentage.
Rule of Thumb
American Council on Exercise (ACE) healthy body fat ranges: Men 14-24%, Women 21-31%. Athletes typically carry 6-13% (men) or 14-20% (women). Body fat above 25% for men or 32% for women is classified as obese by most clinical standards.
Example Calculation
Male, 180 lbs, waist 34", neck 15": using the U.S. Navy formula, estimated body fat = 18.2% — within the fitness category (14-17% for men by ACE standards). He carries approximately 32.8 lbs of fat mass and 147 lbs of lean mass.
Key Facts
- •DEXA (dual-energy X-ray absorptiometry) is the gold standard for body composition measurement, with error margins of 1-2% (NIH, 2023).
- •The U.S. Navy tape measure method has an accuracy of within 3-4% of DEXA for most people, making it a reliable home assessment tool.
- •Visceral fat (around organs) is more metabolically dangerous than subcutaneous fat; waist circumference above 40" (men) or 35" (women) is a cardiovascular risk marker (AHA).
- •Body fat percentage changes with age; the same BMI at age 40 typically corresponds to 5-6% more body fat than at age 20 (American Journal of Clinical Nutrition).
How to Use
- Enter your height and weight.
- Measure and enter your waist and neck circumference at their narrowest/smallest points.
- Women: also enter hip circumference at the widest point.
- Select biological sex and click Calculate.
Formula
Body Fat % = (495 / Body Density) - 450 (Siri equation) | U.S. Navy: 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76