About Body Fat Calculator
The US Navy method estimates body fat from circumference measurements rather than weight alone. It works because fat distributes predictably: for a given height, a larger waist relative to the neck indicates more fat, and the equation was fitted to that relationship across a large group.
It is more informative than BMI for exactly this reason — it uses where the mass sits, not just how much there is. Two people of identical height and weight can have very different waist and neck measurements, and this will separate them where BMI cannot.
It remains an estimate from a tape measure, typically landing within three or four percentage points of a DEXA scan. That accuracy depends almost entirely on measuring consistently: same places, same tension, ideally the same time of day. Because the errors are consistent too, it tracks change over weeks far more reliably than it reports any single absolute figure.
How to use it
Choose metric or imperial
Switching converts what you have already entered rather than reinterpreting it.
Enter your details
Everything is calculated in your browser as you type. Nothing is sent anywhere.
Read the result in context
Each figure is shown with what the formula can and cannot tell you.