Lean Body Mass Calculator
with Lean Mass & Body Composition Estimates

How lean body mass is estimated

Lean body mass represents total body weight minus fat mass. This calculator estimates lean body mass in two ways. First, it uses classic height-and-weight formulas such as Boer, James, and Hume. Second, if body fat percentage is entered, it calculates lean body mass directly from body composition math.

Because formula outputs can differ slightly, this calculator also shows a blended lean body mass value. That blended value averages the available lean mass estimates and gives a central reference point.

Core structure

Why the formulas differ

Boer, James, and Hume are all classic lean body mass equations, but they are not identical. Each formula uses a slightly different relationship between height, weight, and sex. That means the same person can get slightly different lean mass estimates depending on which formula is applied.

That variation is expected. The formulas are not scan-based measures. They are structured estimates designed to approximate lean body mass from basic anthropometric inputs.

Formula families used here

In these formulas, W is weight in kilograms and H is height in centimetres.

Direct lean mass from body fat percentage

If body fat percentage is known or estimated, lean body mass can be calculated directly from total body weight. This is a straightforward body composition calculation rather than a height-and-weight formula estimate.

That direct value can sometimes differ from the formula-based values. When body fat is provided, the calculator includes that direct lean mass result in the blended estimate to give a broader picture.

Frequently Asked Questions