Body Fat Percentage Calculator

No scales or scanners needed — the US Navy method estimates body fat from neck, waist and (for women) hip circumferences, which is why armed forces have used it for decades.

How the US Navy method works

The method was developed by Hodgdon and Beckett at the Naval Health Research Center in 1984. It exploits a simple observation: fat accumulates preferentially at the waist, while the neck stays comparatively lean. The ratio between those circumferences, scaled by height, correlates well with hydrostatically measured body fat.

All measurements are in centimetres. Women need the hip measurement because female fat distribution is less concentrated at the waist, so waist alone is a poorer predictor.

Measuring properly

The formula is only as good as the tape work, and errors here dominate everything else. A one-centimetre mistake at the waist moves the result by roughly a full percentage point.

• Use a flexible, non-stretch tape. Take every measurement on bare skin.
• Stand relaxed and breathe out normally. Do not suck in.
• Keep the tape snug but not compressing the skin, and level all the way round.
• Neck: just below the larynx, with the tape sloping slightly downwards at the front.
• Waist: men measure at the navel; women at the natural narrowest point.
• Hips: the widest point of the buttocks, feet together.
• Measure three times and average. Always measure at the same time of day — first thing in the morning, before eating, is the most reproducible.

Typical ranges

Women carry more essential fat than men as a matter of physiology — it supports hormonal and reproductive function — which is why every band sits higher. Dropping below the essential threshold is not an achievement; it is a medical risk.

How accurate is it

Compared against hydrostatic weighing, the Navy method has a standard error of about ±3 4 percentage points. That is respectable for a tape measure and useless for chasing a single point of precision.

It is least reliable at the extremes: very lean people and people with high body fat both tend to be mis-estimated, and it cannot account for unusual fat distribution or for very muscular builds where the waist is thick with muscle rather than fat. DEXA remains the practical gold standard, with air displacement plethysmography close behind; both cost money and require a facility.

The useful way to use this tool is longitudinally. Even if the absolute number is off by three points, that error is fairly consistent for the same person, so the change over eight weeks is meaningful even when the absolute value is not.