Lean Body Mass Calculator
Estimate your lean body mass (everything except fat) and fat mass from your height and weight, using the widely cited Boer formula.
Example: with Weight 170 lb · Height 5 ft → Lean body mass (Boer): 128.5 lb.
- Lean body mass (Peters, children)124.5 lb
- Lean body mass (James)130.8 lb
- Lean body mass (Hume)119.9 lb
Computed by the calculator below using its default values. Change any input to see your own numbers.
\ud83d\udcaa Build and keep lean mass
Learn moreWhat lean body mass tells you
Lean body mass is your total weight minus fat — muscle, bone, organs and water. It is useful for setting protein targets, dosing some medications, and tracking whether weight changes are fat or muscle. Men typically carry a higher lean-mass share than women. This uses the Boer formula, a solid estimate from height and weight without a body-composition scan.
How it’s calculated & sources
Boer formula (metric, primary result): men LBM = 0.407 times kg plus 0.267 times cm minus 19.2; women = 0.252 times kg plus 0.473 times cm minus 48.3. Fat mass = weight minus LBM; results converted to pounds.
James formula (shown for comparison): men LBM = 1.1 times kg minus 128 times (kg divided by cm) squared; women LBM = 1.07 times kg minus 148 times (kg divided by cm) squared.
Hume formula (shown for comparison): men LBM = 0.32810 times kg plus 0.33929 times cm minus 29.5336; women LBM = 0.29569 times kg plus 0.41813 times cm minus 43.2933.
Peters formula (used instead of the adult formulas for children age 14 or younger): estimated extracellular volume = 0.0215 times weight-in-kg to the power 0.6469, times height-in-cm to the power 0.7236; lean body mass = 3.8 times that estimated extracellular volume. Peters does not distinguish by sex.
Benchmark: Boer formula (1984), a standard lean-body-mass estimator; typical lean-mass share about 75 to 90 percent (higher in men, lower at higher body fat). James formula (1976) and Hume formula (1966) are widely cited alternatives that typically agree with Boer within a few pounds for adults. Peters formula (1971) is applicable for children age 14 or younger.
Results update as you type and are general estimates, not personalized advice. Verify with a professional.
Frequently asked questions
Is this as accurate as a DEXA scan?
No — formulas estimate from height and weight and cannot see your actual composition. A DEXA or hydrostatic test is more precise.
Why estimate lean mass?
It helps set protein intake, judge whether weight loss is fat vs muscle, and personalize fitness goals.
Which formula is best?
Boer is a common, well-validated choice; James and Hume are alternatives. They agree closely for most adults.
How much do Boer, James, and Hume disagree?
For most adults at a typical body composition, the three formulas land within a few pounds of each other — none is dramatically more accurate than the others without a body-composition scan. Showing all three side by side gives you a sense of the plausible range rather than one falsely precise number.
What formula should be used for children?
The adult Boer, James, and Hume formulas were not developed for children. For those 14 or younger, the Peters formula — based on estimated extracellular volume — is used instead.