Why circumferences can estimate body fat
The U.S. Navy developed this method in the 1980s as a practical field alternative to skinfold calipers or underwater weighing. It works because waist and neck circumference correlate fairly reliably with body fat across a wide population, even though it can't see fat distribution the way a scan can.
A worked example
For a man at 175 cm tall with a 38 cm neck and 85 cm waist, the formula gives roughly 16.9%body fat — solidly in the "athletic to fit" range. Increase the waist measurement by a few centimetres in the calculator above and watch how sensitive the estimate is to that one number.
Frequently asked questions
How accurate is the tape-measure method compared to other ways of testing?
It's generally within a few percentage points of more expensive methods like DEXA scans or hydrostatic weighing for most people, which makes it a solid free option — though it can be less reliable for people at the extremes of very low or very high body fat.
Where exactly should I measure?
Neck: just below the larynx (Adam's apple), tape sloping slightly downward toward the front. Waist: at the navel, standing relaxed, not after sucking in or flexing. Hip (for women): around the widest part of the hips and buttocks.
Why does this method need different inputs for men and women?
Men and women tend to store fat differently — more around the abdomen for men, more around the hips for women — so the Navy method uses a formula calibrated separately for each, which is why women also enter a hip measurement.
What body fat percentage is considered healthy?
Common reference ranges put 'fit' around 14–17% for men and 21–24% for women, with 'average' running somewhat higher for both — though healthy ranges shift with age and individual factors, so these are general guides rather than strict targets.
This calculator provides an estimate for general informational purposes only and is not a substitute for a clinical body composition test.