Body Fat Calculator

Select the gender option used by the formula, enter age, choose Metric or Imperial, and enter weight and height. Select Calculate for an estimated body-fat percentage. In Metric mode, 1.80 m is entered as 1 meter and 80 centimeters. Check the fields carefully before interpreting the result.

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HOW THE ESTIMATE IS CALCULATED

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This tool uses a BMI-based adult prediction equation: estimated body fat (%) = 1.20 × BMI + 0.23 × age − 10.8 × S − 5.4. BMI is weight in kilograms divided by height in meters squared. The equation codes the male option as S = 1 and the female option as S = 0; these are the source model’s two categories.

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WORKED EXAMPLE

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For the male option, age 30, weight 70 kg, and height 1.75 m, BMI is about 22.86. Substituting those inputs gives an estimated body-fat percentage of about 18.1%. This illustrates the arithmetic, not a recommended target or an individual health assessment.

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ESTIMATE VERSUS MEASUREMENT

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The equation predicts body fat from a small set of inputs. It does not measure fat tissue, show where fat is distributed, or distinguish individual body-composition differences reliably. A result can differ from skinfold, bioimpedance, or other body-composition assessments.

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Use this adult equation as a general reference rather than applying it to children, pregnancy, or an individual medical decision. If the output is implausible, recheck age, units, and height; do not assume a precise-looking percentage is accurate. Discuss individual interpretation with a qualified health professional.

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Formula reference: Deurenberg, Weststrate and Seidell (1991), “Body mass index as a measure of body fatness: age- and sex-specific prediction formulas.”