Body fat calculator
This body fat calculator estimates your percentage from four tape-measure numbers using the US Navy method. It shows the honest range around that estimate too, because the method is roughly four points wide and almost every other calculator hides that.
Body fat calculator
Body fat calculator
Four measurements and your weight. Everything is worked out in your browser — your measurements are never stored or sent anywhere.
Your waist measurement needs to be larger than your neck for this method to work. Worth checking both — the tape should sit flat and unpulled.
The Navy method sits about four percentage points either side of a DEXA scan. That spread is the range above, and it is why we do not show you one confident number.
When you are cutting, lean mass is usually the more useful of the two to watch.
What this cannot tell you is how your metabolism handles the fat you carry. Two people at the same percentage can have opposite fasting insulin, triglycerides and HDL.
What your body fat percentage actually meansThis is an estimate from the Hodgdon-Beckett circumference equations (US Navy, 1984), intended for education and not as a diagnosis. It carries a standard error of roughly four percentage points against hydrostatic weighing. Discuss health decisions with your doctor.
How this calculator works
The US Navy method estimates body density from the ratio between your girth measurements and your height, then converts that to a fat percentage. It needs nothing but a tape measure, which is why it is the most widely used method online. It never measures your fat — it infers it.
Why we show a range
Validated against hydrostatic weighing, this method correlates well but carries a standard error near four percentage points. A single figure to one decimal place implies a precision no tape measure delivers. The range is what the method actually supports.
Put this tool on your own website
Copy the code below — free to use, with attribution.
Frequently asked questions
How accurate is the US Navy body fat calculator?
It correlates well with hydrostatic weighing, around r = 0.87 to 0.90, but its standard error is roughly four percentage points. So a reading of 18 percent means your true value is probably somewhere between 14 and 22. That is good enough to track a direction over months and not good enough to act on a single number.
How do I measure my waist and neck correctly?
Measure your neck just below the larynx with the tape sloping slightly downward at the front. Measure your waist at the navel if you are male, or at the narrowest point if you are female. Keep the tape flat against the skin, do not pull it tight, and breathe out normally rather than holding your stomach in. Measurement-site error is larger than the equation error in practice.
Is this better than a body fat scale?
They are close, and both are estimates. A tape measure has a standard error near four points; a home body fat scale is typically four to eight points off, and its reading swings with how much water you are holding. The tape has the advantage of not caring whether you drank a litre of water an hour ago.
What is a healthy body fat percentage?
For men aged 20 to 39, roughly 8 to 20 percent, and for women in that age group, 21 to 33 percent. The range shifts up a few points every decade. Athletes sit below it as a group, which is normal for them and not a target for everyone else.
Why does the result show two or three categories at once?
Because the categories are narrower than the measurement error. The fitness band for men is four points wide and this method is four points off, so an honest result often touches more than one band. Anyone showing you a single category is hiding that arithmetic.
Do you store my measurements?
No. The whole calculation runs in your browser. Your measurements are never sent to us, never logged and never stored.
A percentage does not tell you how your body handles that fat
Your fasting insulin, triglycerides and HDL say more about whether your fat tissue is getting in your metabolic way than any scan does.