Lean Body Mass Calculator

Overview

This calculator uses the Hume equations to estimate lean body mass from height, weight and sex.

Clinical Significance

Lean mass estimates can support selected pharmacokinetic, imaging and research applications, but direct body-composition methods are more accurate.

When to Use

• Use when a protocol specifically requests Hume lean body mass.
• Use as an estimate when direct measurement is unavailable.
• Avoid treating the result as a precise measure of muscle mass.

How It Is Calculated

• Hume male: 0.32810 × weight + 0.33929 × height − 29.5336; female: 0.29569 × weight + 0.41813 × height − 43.2933.
• Weight is entered in kilograms and height in centimetres.

Interpretation

• The result estimates non-fat body mass in kilograms.
• Lean body mass includes water, organs, bone and muscle.
• Equation performance varies across populations and extremes of size.

Worked Example

A 170 cm, 70 kg female has an estimated Hume lean body mass of approximately 48.5 kg.

Patient Considerations

• Hydration, oedema, ethnicity, age, pregnancy and body-size extremes can affect validity.

Limitations

• The result is not a direct body-composition measurement.
• The original sample was small.
• The formula uses binary sex categories.

Clinical Pearls

• Specify the equation when documenting the result.
• Use DXA or another validated method when accurate body composition is required.
• Do not equate lean body mass with skeletal muscle mass.

Common Mistakes

• Interpreting the estimate as measured muscle mass.
• Using the wrong height units.
• Using the equation outside adult populations without validation.

Evidence Base

Hume developed sex-specific equations from height and weight against an indirect lean-mass reference method.

References

1. Hume R. Prediction of lean body mass from height and weight. J Clin Pathol. 1966;19:389–391. — Original open-access publication of the Hume equations.