Body Fat Percentage Calculator

The estimate uses the Deurenberg equation, published in 1991, which predicts body fat from BMI, age and sex: body fat % = 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. BMI is itself weight ÷ height², so what the calculator really needs is your height, weight, age and sex — no tape, no calipers. From the percentage it derives fat mass (weight × body fat %) and lean mass (weight minus fat mass). Those two are arithmetic performed on the estimate, not second, independent measurements: if the percentage is off, both are off with it. That convenience is the formula's entire selling point. It is also the source of every limitation below.

Read the equation again and notice what is missing: anything about your actual body. Because the only inputs are BMI, age and sex, any two people who share those three values get the same answer. A competitive powerlifter and a completely sedentary person of identical height, weight, age and sex receive identical body-fat percentages from this formula — which is plainly wrong for at least one of them, and the equation has no way of telling which. This is not something better arithmetic could fix. Deurenberg is a regression fitted to a population: it describes the average relationship between BMI and fatness across a large sample. Applied to one person, it returns what someone with those characteristics typically looks like, not what you look like. The error is largest exactly where people care most — it reads too high in very muscular people, and it can read too low in people carrying little muscle and a lot of fat.

It is worth being blunt here: there is no body-fat classification with the authority of the WHO BMI table. No single set of internationally agreed cut-offs maps a body-fat percentage onto a risk category the way BMI bands do. What circulates instead are ranges from assorted fitness and clinical sources — commonly around 10–20% for men and 18–28% for women, with athletes lower and the bands drifting upward with age. The sex difference is real and structural: essential fat, the fat required for normal physiological function, is higher in women. So a percentage from this page is best read as a rough position, not a grade. Comparing an estimate against an unstandardised band and drawing a conclusion about your health asks for more precision than either can supply.

If you need a number instead of an inference, body fat has to be measured — and every method carries its own error. Skinfold calipers sample subcutaneous fat at a few sites and depend heavily on the skill of whoever holds them. Bioelectrical impedance — the scales and handheld devices — infers composition from how a small current passes through the body, and is sensitive to hydration, recent meals and recent exercise. DEXA, air-displacement plethysmography and hydrostatic weighing are the reference methods, and are correspondingly harder to get to. Whichever you use, the reliable signal is the trend taken the same way under the same conditions. A single reading from any of them — including this one — carries far more uncertainty than the displayed decimal place implies.

The equation was derived in adults, so it does not apply to children or teenagers, whose body fat changes systematically through growth and who are assessed on age- and sex-specific references. It does not apply during pregnancy. Very muscular people, people with significant fluid retention, and anyone at the extremes of the BMI range all sit outside the region where the underlying relationship holds well. Body-fat percentage is a descriptive measurement, not a goal in itself, and it is not an appearance metric. If a figure here concerns you, the useful next step is a conversation with a physician or a registered dietitian who can weigh lab work, history and the whole picture. This page computes an estimate and explains how much confidence it deserves. It does not tell you what percentage to aim for, what to eat, or how to train.