Lean Body Mass Calculator
Lean body mass (LBM) is the portion of your total body weight that is not fat: it includes skeletal muscle, bone, organs, water, and other tissues. Knowing your LBM is useful for estimating metabolic rate, calibrating nutrition targets, tracking the effects of exercise programmes, and (in clinical settings) calculating weight-based drug doses for medications that distribute primarily into lean tissue. This calculator uses two established regression formulas: the Boer formula (1984, American Journal of Physiology) and the James formula, both validated against direct measurement techniques. Enter your weight in kilograms, height in centimetres, and sex. You can optionally enter a body fat percentage from a DEXA scan, bioelectrical impedance analyser, or skinfold calipers: if provided, the calculator will also show your fat mass and a directly measured LBM, which is more accurate than either formula estimate. Results are shown for both formulas so you can see the range of estimates. LBM as a percentage of total body weight (from the Boer formula) is also displayed as a useful body composition indicator.
LBM (Boer): -- kg — LBM (James): -- kg
Formulas used
Two published regression formulas are used. Both take weight in kg and height in cm as inputs.
Boer formula (male): LBM = 0.407 × weight + 0.267 × height - 19.2
Boer formula (female): LBM = 0.252 × weight + 0.473 × height - 48.3
James formula (male): LBM = 1.1 × weight - 128 × (weight / height)^2
James formula (female): LBM = 1.07 × weight - 148 × (weight / height)^2
If body fat % is given:
Fat mass (kg) = weight × (body_fat_pct / 100)
LBM (measured) = weight - fat_mass
Worked example (Boer, male)
75 kg male, 175 cm:
- LBM = 0.407 × 75 + 0.267 × 175 - 19.2
- LBM = 30.525 + 46.725 - 19.2 = 58.05 kg
- LBM as % = 58.05 / 75 × 100 = 77.40%
Typical lean body mass ranges
| Sex | LBM % of total weight (typical range) | Notes |
|---|---|---|
| Male (average adult) | 75% to 85% | Higher muscle mass; athletes may exceed 85% |
| Female (average adult) | 65% to 75% | Higher essential fat proportion physiologically |
These ranges are approximate. LBM varies with age (declining after around 30 due to sarcopenia), fitness level, and training history. Body composition analysis from a DEXA scan provides a more precise measurement.
Clinical uses of lean body mass
In pharmacokinetics, drugs that are hydrophilic (water-soluble) and do not distribute well into adipose tissue are often dosed on LBM or ideal body weight rather than total body weight. Examples include aminoglycosides, vancomycin, and digoxin. Dosing on LBM in obese patients prevents over-dosing because the extra fat mass does not significantly increase the drug's volume of distribution. Always follow prescribing guidance and consult a clinical pharmacist for drug dosing decisions.
Lean body mass: frequently asked questions
What is lean body mass?
Lean body mass (LBM) is the total weight of your body minus the weight of all body fat. It includes the mass of bones, muscles, organs, blood, and water. LBM is used in clinical settings to calculate drug doses, estimate metabolic rate, and assess nutritional status. It differs from fat-free mass in that fat-free mass excludes all lipids, whereas LBM includes essential fat stored within organs and the nervous system.
What is the Boer formula?
The Boer formula was published in 1984 by P. Boer in the American Journal of Physiology. It estimates LBM from weight and height. For males: LBM = 0.407 x weight (kg) + 0.267 x height (cm) - 19.2. For females: LBM = 0.252 x weight (kg) + 0.473 x height (cm) - 48.3. It is commonly used in pharmacy and clinical medicine for drug dosing calculations.
What is the James formula?
The James formula, described by W.P.T. James and colleagues, estimates LBM using weight and the square of the ratio of weight to height. For males: LBM = 1.1 x weight - 128 x (weight/height)^2. For females: LBM = 1.07 x weight - 148 x (weight/height)^2. Height is in centimetres in these formulas. The James formula tends to underestimate LBM in obese individuals.
Which formula is more accurate?
Neither formula is universally superior. Both are regression-based estimates derived from population studies and will vary from direct measures such as DEXA scanning or underwater weighing. The Boer formula is generally preferred in clinical pharmacokinetics. If you have measured body fat percentage (from a DEXA scan, bioelectrical impedance, or skinfold calipers), the direct calculation (LBM = weight x (1 - body fat fraction)) will be more accurate than either formula.
Why is lean body mass important?
Lean body mass matters for several reasons. In clinical medicine, drug doses for drugs with low lipid solubility (such as certain antibiotics and many renally-cleared drugs) are based on LBM or ideal body weight rather than total body weight. In fitness, tracking LBM alongside total weight reveals whether a training or diet intervention is preserving muscle. In nutrition, LBM drives basal metabolic rate: the more lean mass you carry, the higher your resting energy expenditure.
Official sources
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984;247(4 Pt 2):F632-F636. DOI link.
- NIH body composition and obesity research: NIDDK Overweight and Obesity.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General information only, not medical advice.