Body Fat Percentage Calculator (US Navy Method)
This calculator estimates body fat percentage from circumference measurements using the US Navy method — you need your height, waist and neck, plus hip for women. It is accurate to roughly plus or minus 3 percent for most people, which is far better than BMI at distinguishing muscle from fat. Men typically fall between 10 and 20 percent, women between 18 and 28 percent.
What is body fat calculator?
Body fat percentage is the share of your total mass that is fat rather than bone, muscle, organs or water. Unlike BMI, it separates the two things people actually care about.
Essential fat — the minimum needed for normal physiological function — is around 3 to 5 percent for men and 8 to 12 percent for women. Going below that is genuinely dangerous.
The US Navy method was developed because the military needed a fast, cheap way to screen large numbers of personnel without specialised equipment. It is not as precise as a DEXA scan, but it needs only a tape measure.
How body fat percentage is estimated
The US Navy circumference method uses logarithms of your height and girth measurements. It was validated against underwater weighing and tends to slightly underestimate body fat in very lean people and overestimate it in people carrying fat unusually.
Men: BF% = 495 ÷ [1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)] − 450
Women: BF% = 495 ÷ [1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)] − 450
(all measurements in centimetres)Source: US Navy circumference-based body fat estimation equations.
How to use this calculator
- Measure your waist at the navel, standing relaxed, after breathing out normally.
- Measure your neck just below the larynx, with the tape slightly flared at the narrowest point.
- Women: measure hips at the widest point, feet together.
- Take each measurement twice and use the average. Measure in the morning before eating for consistency.
- Keep the tape snug but not digging in — pulling tight is the most common source of error.
Frequently asked questions
What is a healthy body fat percentage?
For men, roughly 10 to 20 percent is a healthy range, with athletes often between 6 and 13. For women, roughly 18 to 28 percent is healthy, with athletes between 14 and 20. Below essential levels is unsafe.
How accurate is the tape measure method?
Typically within about 3 percent of methods like hydrostatic weighing for the average person. It is considerably more informative than BMI but less precise than DEXA or a Bod Pod scan.
Why do I need different measurements for men and women?
Men and women store fat in different patterns, so the equation for women adds hip circumference to capture lower-body fat distribution that the male formula would miss.
Do smart scales give better results?
Consumer bioelectrical impedance scales are usually less accurate than this method and are highly sensitive to hydration. They are useful for tracking trends, not for absolute values.
How often should I measure?
Once every two to four weeks, at the same time of day. Day-to-day swings in hydration and food volume will drown out real changes if you measure daily.
Related calculators
- BMI Calculator — Free BMI calculator for metric and imperial units. Instantly see your body mass index, which weight category you fall into, and your healthy weight range.
- Ideal Weight Calculator — See your estimated ideal weight using the Devine, Robinson and Hamwi formulas, plus the BMI-based healthy weight range for your height.
- Protein Intake Calculator — Calculate your daily protein target in grams based on body weight and activity level, with per-meal breakdowns for 3 or 4 meals.
These figures are estimates from population formulas, not medical advice. Individual needs vary. If you are pregnant, managing a medical condition, or under 18, talk to a doctor before changing your diet.