Estimate body fat percentage using the US Navy tape-measure method.
This calculator uses the US Navy method, which estimates body fat from circumference measurements rather than weight alone. For men it uses neck and waist against height; for women it adds the hip measurement. It works because fat distributes in reasonably predictable patterns, so the relationship between those girths and height correlates with overall fat mass. Measure with a flexible tape, snug but not compressing, at the same time of day, ideally in the morning before eating.
It is an estimate, not a measurement. The Navy method is typically within 3 to 4 percentage points of a DEXA scan for most people, but it is less accurate at the extremes, and for very muscular or very lean individuals it can be noticeably off. Its real value is tracking change over weeks rather than pinning down a single true figure. Body fat percentage is also more informative than BMI, which cannot distinguish muscle from fat and will classify many athletic people as overweight.
Usually within about 3 to 4 percentage points of a DEXA scan, which is enough to track direction over time but not precise enough to treat a single reading as exact. Accuracy falls at very low and very high body fat levels.
Broadly, around 8 to 19 per cent for men and 21 to 32 per cent for women is considered healthy, varying with age and by the source consulted. Women carry more essential fat for physiological reasons, so male and female figures are not comparable.
BMI uses only height and weight and cannot tell muscle from fat, so a muscular person is often classed as overweight. Body fat percentage estimates composition directly, which is why the two can point in different directions for the same person.
Mostly measurement variation and normal changes in hydration, food in the digestive tract and time of day. Measure under the same conditions each time and judge the trend across several weeks rather than reacting to a single reading.