Body Fat Calculator
Estimate body fat from tape measurements.
Runs entirely in your browser — nothing you enter is uploaded or sent to a server.
A tape measure is not a body scan. This is the US Navy circumference estimate, and published comparisons against DEXA scanning show it can be several percentage points out in either direction — more so for very lean or very heavy builds, and for anyone whose proportions differ from the sample it was fitted to. It estimates, it doesn't diagnose, and it isn't medical advice. Read our full disclaimer.
About this tool
The US Navy method, developed by Hodgdon and Beckett in 1984, estimates body-fat percentage from a few tape measurements instead of from weight. That's what makes it interesting alongside BMI: because it looks at where you carry girth rather than how much you weigh, a heavily muscled person who reads as 'overweight' on BMI will usually read normally here. It needs your height, neck and waist; the female equation also uses a hip measurement. Give it your weight as well and it will split that into estimated fat mass and lean mass, which is the pair of numbers most people actually wanted. Measurements are in centimetres, and everything is worked out on your device.
Example
A man 178 cm tall with an 86 cm waist and a 40 cm neck comes out at about 15.7% body fat. At 70 kg that's roughly 11 kg of fat and 59 kg of lean mass.
How to use
- 1Choose which form of the equation to use — the female version includes a hip measurement.
- 2Measure with a tape held snug but not tight, against skin, at the end of a normal breath out.
- 3Enter height, neck and waist (and hip), all in centimetres.
- 4Add your weight to see the estimate split into fat and lean mass.
Features
- The US Navy circumference method, with the male and female equations.
- Fat mass and lean mass in kilograms when you supply your weight.
- Descriptive bands rather than a verdict on the number.
- Tells you plainly when a set of measurements can't produce an answer.
Frequently asked questions
Where exactly do I measure?
Neck: just below the larynx, with the tape sloping slightly down at the front. Waist: at the navel for men, at the narrowest point for women. Hip: at the widest point of the buttocks. Keep the tape level, snug against the skin without compressing it, and take the reading at the end of a normal exhale.
Why does this disagree with my BMI?
Because they measure different things. BMI is weight against height and can't tell muscle from fat. This method reads girth, so someone lean and muscular can be flagged overweight by BMI and land in a normal band here. When the two disagree, that disagreement is usually the useful information.
How accurate is the Navy method?
It's a regression fitted to a large but specific population. Compared against DEXA it's typically within a few percentage points for average adults and drifts further at the extremes of leanness or size. It is best used to track change over weeks in your own measurements, where a consistent method matters more than absolute accuracy.
Why does it ask for a hip measurement only for the female equation?
The two published equations use different inputs. The female form uses waist plus hip minus neck, because hip circumference carries more information about fat distribution in the sample it was derived from. The male form uses waist minus neck alone.
It says my measurements can't produce an answer.
The formula takes the logarithm of your waist minus your neck (plus hip, for the female version). If that figure comes out at zero or below, there's no valid result — it usually means two measurements have been swapped, or one was entered in the wrong unit.
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