Lean Body Mass Calculator

Estimate your fat-free mass (muscle, bone, water, organs).

Select units, enter details, and calculate.

LBM estimates based on these formulas are less accurate than direct composition measurements (DEXA, etc.). Results vary between formulas.

Estimating Lean Body Mass (LBM)

Lean Body Mass (LBM), also known as fat-free mass, represents the weight of everything in your body *except* fat. This includes muscle, bone, water, organs, and connective tissue. Knowing your LBM is often more informative for fitness and health tracking than body weight alone, as changes in LBM can reflect muscle gain or loss.

This calculator uses several common formulas based on height, weight, and gender to *estimate* your LBM.

How to Use

  1. Select Metric or Imperial units.
  2. Select your biological Gender.
  3. Enter your current Weight.
  4. Enter your Height.
  5. Click "Calculate Lean Body Mass".

The results will show your estimated LBM (in both kg and lbs) according to different formulas (typically Boer, James, and Hume). It may also calculate an estimated Body Fat Percentage based on the LBM result.

Common LBM Formulas

These formulas use weight (W in kg) and height (H in cm):

  • Boer Formula:
    • Male: LBM = (0.407 * W) + (0.267 * H) - 19.2
    • Female: LBM = (0.252 * W) + (0.473 * H) - 48.3
  • James Formula:
    • Male: LBM = (1.1 * W) - 128 * (W / H)²
    • Female: LBM = (1.07 * W) - 148 * (W / H)²
  • Hume Formula:
    • Male: LBM = (0.32810 * W) + (0.33929 * H) - 29.5336
    • Female: LBM = (0.29569 * W) + (0.41813 * H) - 43.2933

*(The calculator performs necessary unit conversions before applying the formulas.)*

Interpreting LBM & Body Fat %

LBM is useful for:

  • Tracking muscle gain or loss during fitness programs.
  • Setting more accurate calorie/macro targets (as muscle burns more calories than fat).
  • Understanding body composition beyond just weight.

The **Body Fat Percentage** is calculated simply as: `((Total Weight - LBM) / Total Weight) * 100%`.

Accuracy Limitations

Formulas based only on height, weight, and gender provide *estimates*. They do not account for variations in bone density, muscle mass relative to height (e.g., athletes vs. sedentary individuals), or hydration levels. More accurate methods include DEXA scans, hydrostatic weighing, or multi-point skinfold caliper measurements performed by a trained professional.

Use these results as a general guideline and track changes over time rather than focusing on the absolute number.