Body fat calculator
Estimate body fat percentage from a tape measure, with an honest note on how accurate that is.
- Runs in your browser — nothing you enter is uploaded
- No sign-up, no quotas, free to use as often as you like
How it works
Body fat percentage tells you something that weight alone cannot, which is why people look for it. The honest position is that every method you can use at home is an estimate, and this one is a reasonable estimate with known limits — stated below rather than buried.
The method
The US Navy circumference formula, which estimates body fat from the ratio between your waist and your neck, scaled by height — and additionally the hip for the female formula. It exists because it needs only a tape measure, which is also why it is the method most calculators use.
How accurate it really is
Typically within about three to four percentage points of a DEXA scan, and less reliable at the extremes — very lean and very heavy people are both estimated poorly. It cannot distinguish muscle from fat around the waist, so a muscular midsection reads as fat. Use it to track a direction over weeks, not to pin down a number.
Measuring properly
Measure at the end of a normal breath, with the tape snug but not compressing. Waist at the navel, neck just below the larynx, hips at the widest point. Measure at the same time of day each time, because a full stomach and a day's water shift the numbers more than real change does.
The categories
The bands shown are the commonly published ranges, and they differ between the male and female formulas because typical essential fat differs. They are conventions, not diagnoses.
Not medical advice
This is arithmetic on a tape measure. It is not a diagnosis, not a health assessment and not a substitute for talking to a doctor.
Body fat calculator — questions
How accurate is it?
Usually within three to four percentage points of a DEXA scan, and worse at very low and very high body fat. It is best for tracking change rather than for a precise figure.
Why does it ask for a hip measurement?
Only the female formula uses it — that is how the US Navy method is defined.
Can I use inches?
Yes. Choose inches and enter everything in inches; the conversion is handled.
Why did my number jump between days?
Measurement variation, food and water shift the result more than real change. Measure consistently and compare over weeks.
Is this medical advice?
No. It is an estimate from measurements, not a health assessment.