Body Fat Calculator
Estimate your body fat percentage with the US Navy circumference formula, see how much of your weight is fat and how much is lean mass, and find where you sit on the ACE category chart. Metric and imperial units are both supported.
Navy circumference estimates land within about 3–5 percentage points of a DEXA scan; where you place the tape matters more than which calculator you use.
Formula and calculation
Worked example
A 30-year-old man, 180 cm and 70 kg, measured with a 37 cm neck and an 85 cm waist: body fat % = 495 ÷ (1.0324 − 0.19077×log₁₀(85 − 37) + 0.15456×log₁₀(180)) − 450 = 16.9%, which puts him in the fitness band. That works out to about 11.81 kg of fat and 58.19 kg of lean mass. The BMI-based comparison estimates 16.6%.
Measuring so the number means something
The tape does more damage to accuracy than the formula. Measure first thing in the morning, before eating, with the tape flat against bare skin — snug enough not to slip, never compressing. Keep it horizontal all the way around, check yourself in a mirror at the back, and measure at the end of a normal exhale rather than holding your breath in. Take each measurement twice and average them; a 1 cm slip at the waist moves the result by half a percentage point or more. What matters most is repeating the same routine, so the trend over weeks is comparable even if the absolute number is a few points off.
What the results mean
- Body fat
- Estimated body fat percentage from the US Navy circumference formula — the share of your body weight that is fat.
- Category
- Where your percentage falls on the American Council on Exercise chart: essential fat, athletic, fitness, average or obese. The thresholds differ for men and women.
- Fat mass
- Kilograms of your body weight that are fat, calculated from your percentage and your weight.
- Lean mass
- Kilograms of everything else — muscle, bone, organs and water. This is the number that carries strength and most of your resting metabolism.
- Fat mass (imperial)
- The same fat mass in pounds.
- Lean mass (imperial)
- The same lean mass in pounds.
- BMI
- Body mass index from your height and weight, the same figure the BMI Calculator returns. It is shown here so you can see how often BMI and body fat disagree.
- BMI-based estimate
- Body fat percentage predicted from BMI, age and sex with the Deurenberg equation. It needs no tape measure, but it cannot tell muscle from fat, so treat it as a second opinion rather than a better answer.
Frequently asked questions
How accurate is the Navy body fat method?
Expect to land within about 3–5 percentage points of a DEXA scan, and closer to that in the middle of the range. The formula was built for military personnel, so it is less reliable at very low or very high body fat, and for people who carry fat unusually around the waist. The direction your number moves over a month is more trustworthy than the number itself.
Where exactly should I measure my waist?
Men: horizontally around the waist at the level of the navel. Women: at the narrowest point of the waist, usually just above the navel. Either way, breathe out normally and read the tape without pulling it tight — a compressed waistline can cost you a percentage point or more.
What is a healthy body fat percentage?
For men, 14–24% covers the fitness and average bands on the ACE chart, with roughly 18–24% being typical for adult men. For women, 21–31% is the comparable range. Women carry more essential fat for reproduction, which is why their healthy band sits about 10 percentage points higher than men's.
Why does the calculator ask for a hip measurement?
Only the women's Navy formula uses it — hip circumference plus waist and neck predicts body fat far better in women than waist and neck alone. If you selected male, the field is ignored. Hip is measured around the widest point of the buttocks, with the tape level.