THE NUMORIX GUIDE
How to use the Lean Body Mass Calculator
Last reviewed September 14, 2026
What this calculator does
The engine calculates Boer lean body mass as 0.
Formula and method
The engine calculates Boer lean body mass as 0.407 * weight + 0.267 * (height * 100) - 19.2 for male or 0.252 * weight + 0.473 * (height * 100) - 48.3 for female. It also calculates a James polynomial and estimates body fat as (weight - Boer) / weight * 100. The UI displays the Boer value, not the James value, as its main lean-mass result.
Variables and inputs
The UI labels weight in kilograms and height in centimeters, with a male or female option. The engine multiplies the entered height by 100 before the Boer formula, so its code path effectively expects the height argument in meters even though the component label says cm. Weight is used in kg.
Worked example
Using the visible defaults of 70 kg, 175 cm, and male: the engine treats height as 175 * 100 = 17,500 in the Boer term, producing 0.407 * 70 + 0.267 * 17,500 - 19.2 = 4,681.79 kg and body fat = (70 - 4,681.79) / 70 * 100 = -6,588.27%. James independently gives 72.97 kg. Entering 1.75 instead would make the Boer result about 56.02 kg, illustrating the unit mismatch.
How to interpret the result
The formulas are intended as estimates of lean body mass, but the current UI-to-engine height mismatch makes the visible default output nonphysiological. The negative body-fat percentage is a code-path warning, not a body-composition finding.
Common mistakes to avoid
Do not interpret the displayed default as a real result. The UI says centimeters, while the Boer implementation multiplies the input by 100; verify the height convention before using any output. Lean body mass also includes nonmuscle tissue and is not a direct muscle measurement.
Assumptions and limitations
The current implementation has a unit mismatch between the height label and the Boer formula path, exposes James without displaying it as the headline value, and does not validate body-fat plausibility. Formula estimates also vary with sex profile, body shape, and population. Do not use this route for dosing, diagnosis, or a treatment decision.