Body Fat Calculator
This calculator uses the US Navy circumference method, which estimates body fat percentage from tape measurements. It is the most accurate of the tape-based approaches, needs no equipment beyond a tape measure, and — importantly — is repeatable, which is what makes it useful for watching a trend.
Your result
Fill in the fields on the left and your result appears here.
How the Navy method works
The method exploits a consistent relationship between where circumference accumulates and overall body fat. For men it uses the difference between waist and neck; for women it adds hip circumference, because fat distribution differs enough that a separate equation is needed.
Those differences are combined with height in a logarithmic equation, which is why the result is not a simple ratio and why measuring accurately matters more than it might appear.
- Measure with the tape snug but not compressing the skin, and keep it level all the way round.
- Measure the waist at the navel, and the neck just below the larynx with the tape sloping slightly downward at the front.
- For women, measure the hips at the widest point.
- Measure at the same time of day under the same conditions each time — first thing in the morning is the most consistent.
- Take each measurement twice and use the average. Tape placement is the largest source of variation.
Track it, don't recalculate it.
Pep AI logs your weight, meals and protein alongside your schedule, so the numbers on this page turn into a trend instead of a one-off. Free on iOS and Android.
How much to trust the number
Against a DEXA scan, the Navy method typically lands within a few percentage points, with the error varying by body type — it tends to be less accurate at the extremes of the range and for people whose fat distribution is unusual for their sex.
That makes the absolute figure a rough guide and the trend the genuinely useful output. If you measure consistently, a change of several percentage points over months is real information even if the starting number was a couple of points off.
The practical advice is to pick one method and stay with it. Comparing a Navy estimate against a bioimpedance scale reading against a DEXA result produces three different numbers and no useful conclusion, because the differences between methods are larger than the changes you are trying to detect.
Frequently asked questions
This calculator is general information for healthy adults, not medical or dietary advice. It applies published population formulas and cannot account for your clinical situation. Where a clinician has set you a target, that target replaces this one.
Built by the Pep AI team.