Body Fat Calculator
Estimate body fat percentage from a few tape-measure readings using the US Navy circumference method — no callipers, no scales with electrodes, and nothing sent off your device.
How to use the Body Fat Calculator
- Choose your sex — the formula uses different coefficients — and whether you are working in centimetres or inches.
- Measure your height, your neck just below the larynx, and your waist at the navel, keeping the tape level and snug but not tight. Women also measure the hip at its widest point.
- Optionally add your weight to see the estimate split into fat mass and lean mass, then read your percentage and the range it falls into.
About the Body Fat Calculator
The US Navy formula was developed so that body composition could be assessed with nothing but a tape measure. It works because fat is not distributed evenly: the ratio between the neck and the waist (and the hip, for women) tracks total body fat reasonably well across a large population. Reasonably well is the important phrase — published error against a DEXA scan is typically a few percentage points either way, and it can read badly for very lean or very muscular people. What it is genuinely good at is showing a direction of travel when you measure the same way every few weeks. It is a screening estimate rather than a clinical measurement, so treat any surprising result as a reason to speak to a doctor or a registered dietitian rather than a conclusion in itself.
Frequently asked questions
How accurate is the US Navy body fat formula?
It typically lands within a few percentage points of a DEXA scan for people of average build, and is less reliable at the extremes — very lean, very muscular or very heavy. Measuring consistently matters more than the absolute number.
Where exactly do I measure my waist and neck?
Measure the neck just below the larynx with the tape sloping slightly down at the front, and the waist horizontally at the navel. Breathe out normally and do not pull the tape tight, or the result will read low.
What is a normal body fat percentage?
Reference ranges differ by sex and source. Broadly, men sit around 14–24% and women around 21–31%, with athletes lower and the essential minimum much lower again. Ranges also shift with age, so treat the bands as rough guides.
Why do I need to enter my sex?
Women carry more essential fat, largely in the hip and thigh area, so the formula uses different constants and adds the hip measurement. Using the male formula for a woman produces a significant underestimate.
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