Lean Body Mass Calculator
Three published prediction equations, side by side, rather than one formula presented as if it were exact.
Average of three formulas
133.7 lb
Boer
135.6
James
138.5
Hume
126.9
How each formula is calculated
All three take weight in kilograms and height in centimeters, and split by sex:
Boer (male): 0.407w + 0.267h − 19.2
James (male): 1.10w − 128(w/h)²
Hume (male): 0.3281w + 0.33929h − 29.5336
Boer P (1984), Am J Physiol; James WPT (1976), "Research on Obesity," HMSO; Hume R (1966), J Clin Pathol. Female coefficients differ per formula and are used automatically when "female" is selected above.
Worked example: male, 200 lb (90.7 kg), 5'11" (180.3 cm)
Boer: 145.2 lb. James: 148.5 lb. Hume: 135.4 lb. Average: 143.0 lb. Enter these same numbers above and the tool matches.
Frequently Asked Questions
Why three formulas instead of one?
None of them measure lean mass directly -- only a body-composition scan (DEXA), hydrostatic weighing, or bioimpedance does that. Boer, James and Hume each predict it from height and weight using a different regression dataset, and they don't always agree. Showing all three, the same approach this site's 1RM calculators take, is more honest than picking one and hiding the disagreement.
Which formula is most accurate?
There's no universal answer -- accuracy depends on how closely your build matches the population each formula was derived from. Boer (1984) and Hume (1966) are the two most frequently cited in clinical literature; James (1976) tends to run lower for leaner, more muscular builds. The average of all three is a reasonable single number if you need one.
What's the difference between lean body mass and fat-free mass?
In practice, these terms are often used interchangeably, including in this calculator. Technically, "fat-free mass" excludes all fat, while "lean body mass" traditionally includes a small amount of essential fat (in cell membranes, organs, bone marrow); the formulas here, built from height/weight regressions rather than direct tissue measurement, don't distinguish between the two.
How does this relate to FFMI?
FFMI is lean mass divided by height squared, then height-corrected -- so a lean mass estimate from this page is the direct input the FFMI Calculator needs.
Keep going
- Once you have a lean mass estimate, FFMI turns it into a height-normalized score you can compare against published natural-muscularity benchmarks. FFMI Calculator
- Lean mass estimates your muscle; Wilks scores your actual lifted total against other lifters at any bodyweight. Wilks Calculator