Body fat percentage calculator

How to take the measurements

Neck. Just below the larynx, tape sloping slightly down at the front. Do not flex.

Waist. Men measure at the navel. Women measure at the narrowest point of the waist. Tape snug against skin but not compressing it, measured at the end of a normal exhale.

Hips, women only. The widest point around the buttocks.

Measure at the same time of day each time, ideally in the morning before eating. A centimetre of error moves the result by roughly a percentage point, so consistency matters more than precision.

How accurate it is

The US Navy circumference method typically lands within three to four percentage points of a DEXA scan, which is enough to place you in a band and to track direction over time. It is not enough to argue about a single point. Where it struggles is with unusual fat distribution and with very lean or very heavy people, both of which sit outside the population it was fitted on.

Without tape measurements the calculator uses the Deurenberg equation, which estimates body fat from BMI, age and sex. It carries all of BMI's problems, including calling muscular people fat, so treat it as a rough placeholder rather than a measurement.

What the bands mean

Essential fat is the minimum the body needs to function, around 3 to 5 percent for men and 10 to 13 percent for women, and going below it is dangerous rather than impressive. The athletic and fitness bands above it describe what regular training tends to produce. The average band is where most of the adult population sits, and being in it diagnoses nothing.

Why it is more useful than BMI

Because it separates the two things BMI cannot. Lean mass is what supports and stabilises a joint, and fat mass is what loads it. Two people with the same BMI and a fifteen point difference in body fat are in genuinely different positions when it comes to a painful knee, and only one of those numbers can see it.