About the Lean Body Mass Calculator
Lean body mass - everything in your body except fat - is a more useful number than total weight alone for tracking fitness progress, since it reflects muscle, bone, and organs together. Our Lean Body Mass Calculator estimates it using the Boer formula.
How It Works
The calculator applies the Boer formula, which uses your weight and height with different coefficients for men and women, to estimate lean mass without needing body fat measurement equipment like calipers or a DEXA scan.
Formula & Methodology
The Boer formula was derived by statistically fitting weight and height against directly measured lean mass (via more expensive reference methods) across a study population, producing these specific regression coefficients. Notice height carries a much larger coefficient for women (0.473) than men (0.267) - reflecting that height is a relatively stronger predictor of lean mass in women in the population the formula was calibrated against.
Step-by-Step: Calculating It By Hand
- 1Convert weight to kilograms and height to centimeters if needed.
- 2Multiply weight by 0.407 (men) or 0.252 (women).
- 3Multiply height by 0.267 (men) or 0.473 (women).
- 4Add those two results together, then subtract 19.2 (men) or 48.3 (women) for estimated lean body mass.
Examples
Estimating lean mass
A 160 lb (72.6 kg), 5'8" (173 cm) man has an estimated lean body mass around 58.6 kg, meaning roughly 14 kg is estimated fat mass.
Tracking over time
Recalculating after weight changes shows whether the change came primarily from lean mass or fat mass - useful feedback during a diet or training program.
Advantages
- Estimates lean mass without needing specialized body composition equipment
- Shows both lean mass and estimated fat mass for a fuller picture
- Useful for tracking whether weight changes are coming from muscle or fat
- Simple two-measurement input (weight and height)
Common Mistakes
- Treating this formula-based estimate as equivalent to a DEXA scan or other direct measurement
- Not tracking trend over time, which is more informative than any single measurement
- Assuming lean mass changes track linearly with weight changes during a diet or bulk
- Comparing lean mass estimates across different formulas, which can produce different absolute numbers
Edge Cases to Watch For
- Subtracting lean mass from total weight gives an estimated fat mass, but this is a derived figure carrying the combined uncertainty of the lean mass formula itself.
- Regression-based formulas like Boer were calibrated on a specific reference population and can be less accurate for people with body compositions far outside that population's typical range.
- This doesn't distinguish where lean mass sits (muscle versus organs versus bone), only the total non-fat mass.
- For the most accurate lean mass figure, direct methods like DEXA scanning or bioelectrical impedance analysis outperform any weight-and-height-based formula.
Common Use Cases
- Estimating lean body mass without specialized equipment
- Tracking whether weight changes reflect muscle or fat loss/gain
- Setting protein intake targets, which are often based on lean mass
- General fitness and body composition tracking