Body Fat Calculator
Body fat percentage is a more informative measure than weight alone, because it distinguishes the mass you want to keep from the mass you may want to lose. This calculator estimates it from tape measurements using the US Navy circumference method, a long-standing field technique that requires only a tape measure and converts neck, waist and height — plus hip for women — into a percentage.
The method works because fat accumulates predictably around the abdomen for men and around the hips and thighs for women, so circumference ratios correlate with body composition. The logarithmic formulas were derived by regressing circumference measurements against hydrostatic weighing. They are not as precise as a DEXA scan, but they are consistent, repeatable, and free.
Measurement technique decides the accuracy. Measure the neck just below the larynx, sloping slightly downward at the front. For men, measure the waist at the navel; for women, at the narrowest point of the torso, and the hips at the widest point. Keep the tape level and snug without compressing the skin, measure in the morning, and take each site three times and average.
Interpretation is age- and sex-dependent. Essential fat is about 3% to 5% for men and 8% to 12% for women, and the athletic range is roughly 6% to 13% for men and 14% to 20% for women. The American Council on Exercise categories are a useful reference point, but they describe physique, not health, and very low body fat carries its own risks, particularly for women.
Calculate
How the math works
- Men (metric): body fat % = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450.
- Women (metric): body fat % = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450.
- All measurements are converted to centimetres, and the formula is valid for the range of normal human proportions.
- Fat mass = weight × body fat percentage; lean mass is everything else, including muscle, bone, water and organs.
Frequently asked questions
How accurate is the US Navy body fat method?
Where do I measure my waist?
What is a healthy body fat percentage?
Why is a healthy body fat range higher for women?
Can I use this to measure progress?
Is this the same as BMI?
This body fat calculator is an educational estimate from the US Navy circumference method. It is not a medical assessment and is not appropriate for children, pregnant people, or anyone with a condition affecting body composition. Consult a clinician for a proper evaluation.