Body Fat Calculator
This body fat calculator estimates your body fat percentage with the US Navy circumference method, using your height, neck and waist measurements (plus hips for women), and also shows your fat mass and lean mass.
About this tool
This body fat calculator estimates your body fat percentage with the US Navy circumference method, using your height, neck and waist measurements (plus hips for women), and also shows your fat mass and lean mass.
How to use it
- Choose your sex and measurement unit (cm or inches).
- Enter your height and weight.
- Measure and enter your neck, your waist at the navel and, for women, your hips at the widest point.
- Read your estimated body fat percentage, category, fat mass and lean mass.
Good to know
- Men: body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76 (measurements in inches).
- Women: body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387.
- Categories shown for men: under 6% essential, 6–13% athletic, 14–17% fitness, 18–24% average, 25% and above obese; women are about 8 points higher.
- Fat mass = weight × body fat %, and lean mass is the remainder.
- Tape-measure methods are less precise than DEXA scans but are useful for tracking change over time.
Runs entirely in your browser — nothing you enter is uploaded or stored.
Frequently asked questions
How accurate is the US Navy body fat method?
It typically lands within a few percentage points of lab methods for most people, but it can be off for very muscular or very lean bodies. Measuring the same way each time makes it reliable for tracking trends.
How do I measure my waist and neck correctly?
Measure your neck just below the larynx and your waist horizontally at the navel, relaxed and not sucking in. Keep the tape snug but not compressing the skin, and take two readings to check.
What is a healthy body fat percentage?
Commonly used ranges put average men at about 18–24% and average women at about 25–31%, with lower values for athletes. Very low levels, below essential fat, are not healthy.
Why does my body fat change when my weight doesn't?
You can lose fat and gain muscle at the same time, which leaves weight similar while body fat drops. That is why body fat or waist measurements are often more informative than the scale alone.