Body fat calculator
Three ways to estimate body fat without a DEXA scan. The Navy method uses several circumferences and is the most reliable. The Army's 2023 one-site test needs only your waist and weight, and Deurenberg only height, weight and age, both with a wider error.
Body Fat Calculator
The US Navy method estimates body fat percentage from height, neck and waist circumference, plus hip circumference for women. Men typically measure 10 to 20 percent and women 18 to 28 percent, with athletic ranges around 6 to 13 percent for men and 14 to 20 percent for women. Expect roughly 3 percentage points of error against a DEXA scan.
Just below the larynx.
Navy: at the navel for men, narrowest point for women. Army: at the navel for everyone.
Optional for the Navy method — adds the fat/lean mass split. Required for Army and Deurenberg.
Metric or imperial · runs the same code as the app · nothing is sent anywhere
How it works
The US Navy method fits body density from circumferences (Hodgdon-Beckett), then converts it with the Siri equation, BF% = 495 / density − 450. For men the density term uses waist minus neck; for women it uses waist plus hip minus neck. Height enters both.
Deurenberg works off BMI instead: BF% = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. It needs no tape but typically sits 4 to 5 percentage points off a DEXA reading, and it was validated only between a BMI of 18 and 35.
The Army one-site test (AR 600-9, 2023) uses a single waist girth at the navel and bodyweight, in inches and pounds: BF% = −26.97 − 0.12 × lb + 1.99 × waist for men and BF% = −9.15 − 0.015 × lb + 1.27 × waist for women. It replaced the Army's old neck-and-waist tape test because it tracked DEXA as well with fewer measurements.
Tape accuracy drives everything here. Half a centimetre moves the result, so measure on bare skin, keep the tape level and take each measurement twice.
Common questions
How accurate is the Navy body fat method?
Typically within about 3 percentage points of a DEXA scan for most people, which is good enough to track a direction over months. It is less reliable at the extremes, and it assumes a fairly typical fat distribution.
What is the Army one-site body fat test?
Since 2023 the US Army estimates body fat from a single waist measurement at the navel plus bodyweight. It is quicker than the Navy method and, in the Army's own validation against DEXA, about as accurate on average, but with only one girth it cannot account for where else you carry fat.
Why does the female formula need a hip measurement?
Women carry proportionally more fat on the hips and thighs, so waist alone under-reads. The female equation uses waist plus hip minus neck to capture that.
Where exactly do I measure?
Neck just below the larynx with the tape sloping slightly down at the front. Waist at the navel for men, at the narrowest point for women. Hip at the widest point of the glutes. Stand relaxed and do not pull the tape tight.
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These numbers are more useful when something tracks them.
The app runs this same maths against your logged weigh-ins, meals and sessions, so the figure updates itself instead of being a one-off.
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