About

Shifting the focus from weight loss to composition gain is critical for long-term health. This tool calculates Lean Body Mass (LBM) which encompasses muscle, bone, water, and organs. It specifically addresses the needs of bodybuilders by calculating the Fat-Free Mass Index (FFMI). Unlike BMI, FFMI rewards muscle gain. The tool helps users identify their proximity to the theoretical natural limit of muscular development. Knowing these numbers distinguishes true tissue growth from mere fluctuation.

Formulas

If body fat is unknown, the Boer formula approximates LBM based on anthropometry.

LBM_male = 0.407W + 0.267H − 19.2

With known body fat, the calculation is precise.

LBM = Weight × 1 − BF%

Fat-Free Mass Index (FFMI) normalizes this mass for height.

FFMI = LBM_kgHeight_m²

Reference Data

FFMI Score	Classification	Typical Physique
16-17	Below Average	Slight build, low muscle
18-19	Average	General population male
20-21	Excellent	Athletic, well built
22-24	Superior	Elite natural athlete
> 25	Suspicious	Likely enhanced usage

Frequently Asked Questions

Research suggests that an FFMI of 25 is the upper ceiling for natural testosterone production. Scores significantly above this usually indicate the use of anabolic agents.

The Boer formula is statistically derived to estimate lean mass in individuals where body fat percentage is not explicitly known. It is often more accurate than Hume for athletic populations.

Not exactly. LBM includes water, bone, organs, and connective tissue. However, since bone and organ mass are relatively constant, changes in LBM usually reflect changes in skeletal muscle.

Increase muscle mass through hypertrophy training while maintaining or lowering body fat. Gaining fat will not improve FFMI, but gaining muscle will.