The formula
How it works
Estimate your body-fat percentage from a few tape-measure readings using the U.S. Navy method. It needs only your height and a couple of body circumferences — no calipers or scales — and gives a quick, repeatable figure to track over time.
FAQ
How accurate is the tape method?
It is a good estimate, usually within a few percent of a proper scan, and its real strength is consistency. Measure the same way each time and the trend is reliable even if the exact number is not perfect.
Where exactly do I measure?
Measure your neck just below the larynx, and your waist at the navel (for men) or at the narrowest point (for women, who also measure the hips at the widest point). Keep the tape snug but not tight.
What is a healthy body fat percentage?
Essential fat is around 2–5% for men and 10–13% for women, with athletic ranges typically 6–20% for men and 14–24% for women. Averages sit higher, and what counts as “healthy” also depends on age and individual context.
Why is my result different from a DEXA scan or caliper test?
Every method has its own margin of error and measures body fat slightly differently, so results rarely match exactly. The tape method is best used to track your own trend over time rather than to compare against a different test’s absolute number.
Does this method work well for athletes or bodybuilders?
It tends to be less accurate for people with very muscular builds, since a thick, muscular neck or waist can understate body fat. Very lean or very heavily muscled individuals are better served by a caliper test or a scan.
What’s the difference between BMI and body fat percentage?
BMI only compares weight to height and can’t tell fat from muscle, so a muscular person can register as “overweight” on BMI despite having low body fat. Body-fat percentage measures composition directly, which is why the two numbers can tell very different stories for the same person.
What if my measurements give a negative or unusually high number?
A negative or extreme result usually means a measurement was taken incorrectly — most often the waist and neck values are too close together. Re-measure carefully, keeping the tape level and snug, and double-check you used the right units.
About the body fat calculator
This calculator estimates your body-fat percentage using the U.S. Navy circumference method, which the military uses because it needs nothing more than a tape measure. Body-fat percentage is often a better health marker than weight or BMI alone, because it separates fat from muscle and bone. Two people at the same weight can have very different amounts of fat, and this method gives a fast way to estimate which is which.
How to use it
Choose your sex and units, then enter your height and circumference measurements: neck and waist for everyone, plus hips for women. The calculator returns your estimated body-fat percentage and the category it falls into. For instance, a man of 180 cm with a 39 cm neck and 96 cm waist comes out around 23%. Measure first thing in the morning and in the same spots each time so your readings stay comparable.
The formula
For men the U.S. Navy formula is , where is the waist, is the neck and is the height, all in inches. Women use , which adds the hip measurement. Metric inputs are converted to inches first. The logarithms mean the result depends on the ratios between measurements, not their absolute size.
Where it is used
The armed forces use this method for fitness standards because it is cheap and portable, needing only a tape measure. Personal trainers and dieters use it to track progress that the scale can hide — losing fat while gaining muscle can keep weight flat. It is also a useful screening tool, since a high body-fat percentage is linked to greater health risk even at a normal weight, a pattern sometimes called “skinny fat”.