Body Fat Percentage Calculator
Estimate your body fat percentage from a tape measure and a few simple measurements, using the U.S. Navy circumference method, a formula developed for military fitness assessments that's held up well against more expensive body composition tests.
Measured at the navel, standing relaxed.
Your result will appear here
Enter your measurements and click calculate to see your estimated body fat percentage.
Quick Answer
The U.S. Navy method estimates body fat percentage from your height, neck, and waist circumference (plus hip circumference for women), using the gap between waist and neck size as a proxy for fat distribution.
How It Works: Formula & Variables
Men: %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Women: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
All measurements go in as inches. The calculator above converts centimeters automatically if you enter metric units.
Worked Examples
Example: Male, 5'10", 15" neck, 34" waist
Plugging 70 inches height, 15 inches neck, and 34 inches waist into the men's formula gives an estimated body fat of around 17.5%, which falls in the "fitness" category.
Example: Female, 5'5", 13" neck, 30" waist, 40" hip
Using the women's formula with 65 inches height, 13 inches neck, 30 inches waist, and 40 inches hip gives an estimated body fat of around 31%, in the "average" range.
Key Concepts
Essential fat: The minimum body fat needed for basic physiological function, roughly 2-5% for men and 10-13% for women. Going below this range isn't a fitness goal, it's a health risk.
Why body fat differs from BMI: BMI only looks at height and weight. Two people with the same BMI can have very different body fat percentages depending on how much of their weight is muscle versus fat.
Measurement consistency matters: Measure at the same time of day, ideally in the morning before eating, and keep the tape snug but not compressing the skin, for results you can compare over time.
Common Mistakes
Measuring the waist at the narrowest point: The U.S. Navy method calls for measuring at the navel, which is usually wider than the natural waistline. Using the wrong spot skews the result.
Pulling the tape too tight: Compressing the skin gives an artificially small measurement and understates body fat.
Treating the estimate as exact: This method is a solid approximation, not a lab-grade measurement. Track the trend over weeks and months rather than reacting to a single number.
Frequently Asked Questions
It's generally accurate to within 3-4% of body fat measured by more precise methods like DEXA scans, which makes it one of the better tape-measure-based estimates available. It tends to be less accurate for people at the extremes of muscle mass or body shape.
Height, neck circumference, and waist circumference for men. Women also measure hip circumference. Use a flexible tape measure, stand relaxed, and measure the waist at the navel rather than the narrowest point.
The U.S. Navy method uses the difference between waist (or waist plus hip for women) and neck circumference as a proxy for fat distribution. Neck size stays relatively stable regardless of fat gain or loss around the midsection, which makes it a useful reference point in the formula.
No. BMI only uses height and weight and doesn't distinguish fat from muscle. Body fat percentage estimates the actual proportion of your weight that's fat, which is why a muscular person can have a high BMI but a low, healthy body fat percentage.
For men, 14-24% is typically considered the "fitness" to "average" range, with under 14% common among athletes. For women, the equivalent range runs about 21-31%, with under 21% common among athletes. Essential fat, the minimum needed for basic health, is around 2-5% for men and 10-13% for women.