Body fat percentage calculator

How to measure well

Use a flexible tape measure, without squeezing. Measure with your body relaxed, ideally in the morning. The U.S. Navy method estimates body fat from body circumferences: it's less accurate than a skinfold or DEXA scan, but it's practical and useful for tracking the trend over time by always measuring the same way.

Reference values

Rough guide (male / female): essential 2-5% / 10-13%, athletes 6-13% / 14-20%, fitness 14-17% / 21-24%, acceptable 18-24% / 25-31%, obese 25%+ / 32%+. These are general averages: for clinical assessment consult a professional.

Where exactly the tape goes

The neck is measured just below the Adam's apple, with the tape tilted slightly forward and your head not bowed. The waist is measured at navel height for men and at the narrowest point of the trunk for women, at the end of an exhale and without pulling your stomach in. The hips, which are only needed in the female formula, at the widest point of the buttocks, feet together.

One centimetre wrong at the waist shifts the result by about half a percentage point, which is more than many people hope to lose in a month. It is worth measuring twice and taking the average, and always repeating at the same time of day.

Why a tape measure manages to say anything at all

The method does not «see» fat: it exploits the fact that fat is laid down fairly predictably, mostly on the abdomen, while the neck changes very little as weight changes. The difference between the two circumferences, corrected for height, is therefore a good clue to how much fat sits in between.

It works well on the average population and errs more at the extremes. On a very muscular person the wide neck makes them come out leaner than they are; on someone with little muscle the opposite happens. The formulas were built on adult military personnel, so on children, teenagers and pregnant women the result has no meaning.

The absolute value matters less than the direction

Estimates can differ by several points from one method to another: skinfolds, a bioimpedance scale and a DEXA scan rarely give the same number, and bioimpedance in particular changes with hydration, with the hour and with the last meal. Chasing the «true» number is almost always wasted effort.

What does stay reliable is the comparison of the same measurement repeated the same way. If every two weeks, in the morning, with the same tape and at the same points, the value goes down, fat really is going down, even if the number itself sits a little above or below reality. That is why it is worth writing down the circumferences, not only the percentage that comes out at the end.

Nearby tools

BMI calculator uses only weight and height, and for that very reason cannot tell muscle from fat; Waist-to-height ratio looks at the waistline and is a simple, robust risk indicator. For a reference weight there is Ideal weight, and for calories Basal metabolic rate.