What is lean body mass?

Lean body mass is everything in your body other than fat: muscle, bone, organs, body water and other non-fat tissue. It is a body-composition estimate, not a direct measure of muscle alone.

Why does this calculator need sex?

The Boer, James and Hume equations each use different constants for men and women. Selecting sex is therefore required for the equations to produce the intended estimate.

Why do the three formula results differ?

Each equation was developed from a different study population and uses a different mathematical model. Showing the range makes that ordinary variation visible, rather than implying that any single result is exact to the decimal place.

Is lean body mass the same as muscle mass?

No. Muscle is one part of lean body mass, alongside water, bone, organs and other non-fat tissue. A lean body mass estimate cannot tell you how much of it is muscle.

Lean Body Mass Calculator

Lean body mass is the portion of total weight that is not fat. It includes muscle, bone, organs and body water, so it is not the same thing as muscle mass. This calculator compares the Boer, James and Hume equations to give a practical estimate range rather than a falsely precise single number.

Estimate your lean body mass

Enter metric measurements. Runs entirely in your browser.

The three lean mass equations

All three equations use total weight and height, with separate versions for women and men. They provide estimates useful for comparison and trend tracking.

Lean body mass equations by formula and sex
Formula	Women	Men
Boer (1984)	0.252 × weight (kg) + 0.473 × height (cm) − 48.3	0.407 × weight (kg) + 0.267 × height (cm) − 19.2
James (1976)	1.07 × weight (kg) − 148 × (weight ÷ height)²	1.10 × weight (kg) − 128 × (weight ÷ height)²
Hume (1966)	0.29569 × weight (kg) + 0.41813 × height (cm) − 43.2933	0.3281 × weight (kg) + 0.33929 × height (cm) − 29.5336

What lean body mass is used for

Lean body mass is often used as a body-composition reference when tracking training or nutrition goals, because total weight alone cannot distinguish fat from non-fat tissue. It can make progress discussions more useful when body weight stays stable while body composition changes.

Some drug-dosing methods also use estimated lean body mass as one input. Those methods are for qualified professionals using the relevant guidance and individual context; this calculator is for general wellness education and should not be used to make medication decisions.

For nutrition targets, the estimate can be a starting point for comparing protein or energy plans over time. Treat it as a broad reference and focus on sustainable habits rather than chasing a particular number.

How to use the estimate

These equations estimate lean mass from height, weight and sex; they do not measure your tissues directly. Hydration, body shape and the populations used to develop the formulas can all affect how closely an estimate reflects an individual. Comparing results taken under similar conditions is usually more informative than reading too much into a one-time value.

Common questions

What is lean body mass?: Lean body mass is everything in your body other than fat: muscle, bone, organs, body water and other non-fat tissue. It is a body-composition estimate, not a direct measure of muscle alone.
Why does this calculator need sex?: The Boer, James and Hume equations each use different constants for men and women. Selecting sex is therefore required for the equations to produce the intended estimate.
Why do the three formula results differ?: Each equation was developed from a different study population and uses a different mathematical model. Showing the range makes that ordinary variation visible, rather than implying that any single result is exact to the decimal place.
Is lean body mass the same as muscle mass?: No. Muscle is one part of lean body mass, alongside water, bone, organs and other non-fat tissue. A lean body mass estimate cannot tell you how much of it is muscle.