Lean Body Mass Calculator
Estimate your lean body mass using the Boer, James, and Hume formulas.
Estimate your lean body mass (LBM) using multiple established formulas. Results shown side-by-side for easy comparison.
How Lean Body Mass Is Calculated: Boer, James, and Hume Formulas
Boer Formula (1984)
Uses weight and height with sex-specific coefficients: LBM (men) = 0.407W + 0.267H − 19.2; LBM (women) = 0.252W + 0.473H − 48.3 (W in kg, H in cm). Consistently performs well in validation studies for adults of average build and is the primary result shown by this calculator.
James Formula (1976)
Incorporates a weight-to-height ratio correction term that reduces LBM estimates for heavier people. Known to underestimate LBM significantly in individuals with a BMI above 30, where the correction term becomes too aggressive and produces implausibly low values.
Hume Formula (1966)
One of the earliest LBM formulas, derived from isotope dilution studies. Uses similar weight and height inputs to Boer but with different coefficients. Tends to give slightly higher estimates than Boer or James, particularly for women. Useful as a cross-check alongside the other formulas.
Peters Formula (children)
Designed specifically for children aged 13–14 and under, based on estimated extracellular volume: LBM = 3.8 × 0.0215 × W^0.6469 × H^0.7236. Not appropriate for adults — the adult formulas significantly overestimate LBM in children, and Peters significantly underestimates it in adults.
Why Lean Body Mass Matters
Medical dosing and clinical use
LBM is used clinically to calculate doses of medications that distribute primarily in lean tissue, including many chemotherapy drugs, anaesthetics, and antibiotics. Using total body weight overestimates doses in people with higher body fat, with potential toxicity implications. LBM also factors into kidney function estimates (eGFR) and certain nutritional support prescriptions in hospital settings.
Body composition tracking for athletes
LBM is more informative than total weight for anyone building muscle or losing fat. Scale weight can stay the same or rise while body composition improves (fat loss offset by muscle gain). Recalculating LBM regularly shows whether a programme is preserving lean tissue during a fat loss phase, or whether an apparent weight gain is muscle, fat, or water retention. For the most accurate picture, combine LBM with a body fat percentage measurement.
Setting protein and calorie targets
Protein targets and Katch-McArdle BMR calculations both use lean body mass when body fat % is known, rather than total weight. This is more accurate because fat tissue has minimal protein and calorie requirements. For people with higher body fat percentages, total-weight-based calculations can meaningfully overstate protein needs and resting calorie burn. Use the protein calculator to set LBM-based daily targets.
LBM vs muscle mass — an important distinction
Lean body mass is not the same as muscle mass. LBM includes everything that is not fat: muscle, bone, organs, blood, and body water (which alone accounts for ~60% of body weight). Muscle mass typically represents 35–45% of total body weight in healthy adults, or roughly 55–65% of LBM. A high LBM figure reflects overall lean tissue, not just muscle.
Lean Body Mass Worked Example
Male, 178 cm, 85 kg
Boer: LBM = (0.407 × 85) + (0.267 × 178) − 19.2 = 34.6 + 47.5 − 19.2 = 62.9 kg. James: LBM = 1.1 × 85 − 128 × (85/178)² = 93.5 − 32.5 = 61.0 kg. Hume: LBM = (0.3281 × 85) + (0.33929 × 178) − 29.5336 = 27.9 + 60.4 − 29.5 = 58.8 kg. Estimated fat mass = 85 − 61 ≈ 24 kg (28% body fat).
Typical Lean Body Mass Values by Height
| Height | 70 kg body weight | 80 kg body weight | 90 kg body weight |
|---|---|---|---|
| 165 cm | 53 kg LBM | 57 kg LBM | 62 kg LBM |
| 170 cm | 55 kg LBM | 59 kg LBM | 63 kg LBM |
| 175 cm | 56 kg LBM | 60 kg LBM | 64 kg LBM |
| 180 cm | 57 kg LBM | 61 kg LBM | 66 kg LBM |
| Height | 55 kg body weight | 65 kg body weight | 75 kg body weight |
|---|---|---|---|
| 155 cm | 39 kg LBM | 41 kg LBM | 44 kg LBM |
| 160 cm | 41 kg LBM | 44 kg LBM | 46 kg LBM |
| 165 cm | 44 kg LBM | 46 kg LBM | 49 kg LBM |
| 170 cm | 46 kg LBM | 49 kg LBM | 51 kg LBM |
Protein targets from LBM
The general guideline for muscle maintenance is 1.6–2.2 g of protein per kg of LBM per day — not per kg of total body weight. For a man with 60 kg LBM, that is 96–132 g of protein daily. Using total body weight inflates the target for people with significant body fat, while using LBM keeps the target proportional to the tissue that actually needs it.
What LBM tells you that scale weight cannot
Two people at identical body weights can have very different LBM values — meaning their calorie needs, protein requirements, and health risks differ substantially. Someone at 85 kg with 70 kg LBM has a fundamentally different body composition from someone at 85 kg with 55 kg LBM. Tracking LBM over time (particularly during a fat loss phase) confirms whether lean tissue is being preserved or lost.
LBM and basal metabolic rate
Lean body mass is the primary driver of your basal metabolic rate. Fat tissue requires minimal energy at rest; it is lean tissue — muscle, organs, bone — that accounts for most of your resting calorie burn. The Katch-McArdle BMR formula uses LBM directly (BMR = 370 + 21.6 × LBM in kg) and is more accurate than weight-based formulas for people outside the average body fat range.
Using LBM as a fitness metric
During a fat-loss phase, total body weight can stay constant while body composition improves — fat decreases and muscle increases. Tracking LBM alongside body fat percentage reveals this change that the scale misses. A successful cut preserves or increases LBM while reducing fat mass. Monthly LBM measurements give a clearer picture of training effectiveness than weight alone.
Frequently Asked Questions
What is lean body mass?
Lean body mass is the total weight of your body minus fat mass. It includes muscles, bones, organs, blood, and water — everything that is not adipose tissue. It is used in medical dosing, athletic tracking, and nutritional planning because it focuses on the metabolically active tissue that drives most of the body's protein and calorie requirements.
What is a typical lean body mass?
LBM varies significantly with height, sex, age, and fitness level. As a rough benchmark: a 75 kg, 178 cm adult male typically has an LBM of 60–65 kg (80–87% of body weight); a 65 kg, 165 cm adult female typically has around 45–50 kg (70–77%). The formula comparison table in the calculator shows the full range of estimates for your specific measurements.
How accurate are these LBM formulas?
No single formula is universally accurate — each was developed from a specific population. Comparison studies show typical errors of 2–4 kg between formulas for the same individual. The spread of values across the three adult formulas (Boer, James, Hume) provides a practical confidence interval; the true LBM is likely within that range.
Why use LBM instead of total body weight?
Fat tissue has very different metabolic properties from lean tissue — it requires minimal protein, contributes little to resting energy expenditure, and distributes fewer drugs. Using LBM for protein targets, BMR calculations, and clinical dosing produces more accurate results. For people with higher body fat percentages, total weight can significantly overstate these needs.
Evidence & Methodology
How This Page Is Grounded
Method
Compares published Boer, James and Hume height-and-weight equations for estimated lean mass.
Important limitation: These are population equations, not body-composition measurements, and accuracy varies by body size and population.
Primary Sources
Quality Checks
All sex-specific equations and unit conversions are checked with worked examples.
See how sources are selected and corrections are handled in our Editorial & Calculation Methodology, and which automated checks this page has to pass in How We Test.