Free online tool
Body Fat Percentage Calculator
Enter a few tape measurements and get a body fat estimate using the U.S. Navy method.
How the Navy method works
The U.S. Navy developed this formula so that recruits could be assessed with nothing more than a measuring tape. It uses the ratio of waist and neck circumference (plus hip for women) against height to estimate body fat percentage. It's not as accurate as a DEXA scan, but it's remarkably close for most people and can be repeated at home for free.
Getting accurate measurements
Measure at the widest part of your waist (usually around the navel), the narrowest point of your neck (just below the Adam's apple), and — for women — the widest part of the hips. Take each measurement two or three times and average them. Keep the tape snug but not compressing the skin.
+How does this compare to a scale that measures body fat?
Home bioelectrical scales are heavily affected by hydration and often less accurate than a careful Navy-method measurement.
+What's a healthy range?
Broadly, 10–20% for men and 18–28% for women is considered healthy, but athletes and older adults sit outside those ranges.
Estimating body composition with a tape measure, not a scanner
This calculator uses the U.S. Navy circumference method, which estimates body fat percentage from neck, waist, and — for women — hip measurements, combined with height, using logarithmic formulas derived from research correlating those circumferences with body density.
The method was developed for military fitness screening because it needed to be fast, cheap and repeatable across huge numbers of recruits without access to laboratory equipment, and those same properties are exactly why it remains popular for casual home tracking decades later.
Why a tape measure can approximate a body scan
The method works because waist and neck circumference correlate reasonably well with total body fat across large population samples, even though it can't see subcutaneous versus visceral fat separately. Studies comparing it against hydrostatic weighing or DEXA scans generally find it accurate to within about 3 to 4 percentage points for most body types, though it tends to be less reliable for very lean athletes or people with unusual fat distribution.
Worked example
A man who is 178 cm tall with a 90 cm waist and a 38 cm neck plugs those figures into the Navy formula, which typically lands him somewhere in the mid-teens to low twenties percent range depending on exact measurement precision — small measuring errors of even a centimetre can shift the result noticeably.
For a woman, the formula also factors in hip circumference, so two women with identical waist and neck measurements but different hip sizes will get different body fat estimates, reflecting how fat distribution differs on average between sexes.
Comparing methods you might have tried before
Skinfold calipers measure subcutaneous fat directly at several body sites and can be more precise in trained hands, but results vary widely between different people taking the measurement. Bioelectrical impedance scales estimate fat from how electrical resistance moves through your body, but hydration level alone can swing the reading by several percentage points in either direction. The Navy tape method sits in the middle: less precise than a lab scan, but far more consistent between users than calipers or home impedance scales.
A note before you act on the number
Consistent technique matters far more than most people expect: measure at the same time of day, without clothing bulk, and standing relaxed rather than sucking in your stomach. This is a screening estimate meant to track trends over time, not a diagnostic measurement, and it isn't medical advice — don't treat a single reading as a fixed fact about your health.
Tracking change over time matters more than one reading
Because the Navy method has a built-in margin of error, a single measurement session tells you less than a series of measurements taken monthly under the same conditions. A downward trend across several consistent readings is far more meaningful than obsessing over the exact percentage from any one session, especially since day-to-day water retention can shift waist measurements by a centimetre or more.
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