About

Lean Body Mass (LBM) represents the weight of your body minus all adipose tissue (fat). It includes muscle, bone, water, connective tissue, and internal organs. For athletes and medical professionals, tracking LBM is often more critical than total weight because it correlates directly with metabolic rate and drug dosage requirements. Unlike simple BMI, which treats all weight equally, LBM distinguishes between functional tissue and energy storage.

This tool aggregates three distinct, clinically recognized algorithms to provide a weighted average. The Boer formula is widely considered the gold standard for individuals with normal body composition. The James formula is historically significant but can underestimate LBM in obese subjects. The Hume formula offers a middle ground. By analyzing the variance between these methods, users gain a more reliable confidence interval regarding their actual muscle mass versus fat mass.

Formulas

The calculator utilizes the following anthropometric equations (where W is weight in kg and H is height in cm):

Boer Formula (Male):

LBM = 0.407W + 0.267H − 19.2

Boer Formula (Female):

LBM = 0.252W + 0.473H − 48.3

Body Fat Percentage:

BF% = 100 × TotalWeight − LBMTotalWeight

Reference Data

Formula Author	Year	Target Population	Primary Constraint
Boer	1984	General Population	Most accurate for normal BMI ranges.
James	1976	Medical/Pharmacology	Can distort results at very high BMI (>35).
Hume	1966	Clinical	Often used for drug dosing calculations.
Peters	2011	Pediatrics/General	Updated coefficients for modern populations.

Frequently Asked Questions

Each formula was derived from a different study group. The Boer formula (1984) is generally considered the most robust for average body types, while the James formula can skew results for individuals with high body fat percentages. Averaging them provides a safety margin.

No. Lean Body Mass includes everything that is not fat: water, bones, organs, and muscle. skeletal muscle mass is roughly 40-50% of your Lean Body Mass.

Significantly. Since water makes up a large portion of lean tissue, severe dehydration will lower your actual LBM, although these formulas rely on height and weight, so they calculate "expected" LBM based on morphology, not hydration status.

For men, a lean mass of 80-90% (10-20% body fat) is considered athletic. For women, 75-82% (18-25% body fat) is considered fit/athletic. Values vary by age.