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Lean Body Mass (Hume Formula) Calculator

Work out your lean body mass using the classic Hume formula.

How it is calculated

The Hume equation is a linear formula with different coefficients for each sex. For men: LBM = 0.3281 × W + 0.33929 × H − 29.5336. For women: LBM = 0.29569 × W + 0.41813 × H − 43.2933. Here W is body weight in kilograms and H is height in centimetres. Fat mass is then W − LBM, and body fat is (W − LBM) / W × 100, shown with two decimals. Any sex value other than female uses the male coefficients. The tool returns no result if weight or height is empty, zero or negative, or if the formula gives a negative lean mass or one larger than your weight. The equation is a population estimate, not a measurement.

Worked example

A man weighs 80 kg and is 180 cm tall. Weight term: 0.3281 × 80 = 26.248. Height term: 0.33929 × 180 = 61.0722. Sum minus the constant: 26.248 + 61.0722 − 29.5336 = 57.7866, so lean body mass is 57.79 kg. Fat mass is 80 − 57.79 = 22.21 kg, and body fat is 22.21 / 80 × 100 = 27.77%.

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Common mistakes

  • Typing pounds and inches. The fields take kilograms and centimetres, so 176 lb entered as 176 kg gives a wildly wrong lean mass.
  • Leaving sex unselected and assuming a neutral result. Anything other than female falls back to the male coefficients, which gives a higher lean mass for the same measurements.
  • Reading the body fat percentage as a measurement. It is only weight minus an estimate, so very muscular or very frail people can be far off.
  • Comparing the result with the James or Boer formulas and expecting the same figure. Each equation was fitted to a different group and they disagree by several kilograms.
  • Entering height in metres (1.8). A value this small is not a plausible height in centimetres, and the tool returns no result.

Sources

About this calculator

Lean body mass is total body weight minus fat mass — everything that isn't fat: muscle, bone, organs, and water. The Hume formula, published in 1966, is one of the classic equations for estimating it without specialized equipment, using just weight, height, and sex, with separate coefficients for men and women that reflect typical differences in body composition between the sexes.

Lean body mass matters clinically because many drug dosages — especially for anesthesia and chemotherapy — are calculated per kilogram of lean mass rather than total body weight, since fat tissue doesn't metabolize most drugs the same way lean tissue does. It's also used in sports science and body-composition tracking to separate muscle changes from fat changes. Weight, height, and sex go in; your estimated lean body mass, using the Hume equation, comes out.

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