AtlasCalcsUtility Calculation Suite
2026-09-14 11 min

Lean Body Mass Calculator

Estimate lean body mass with Boer, James, and Hume formulas. See average LBM, body-fat percentage, fat mass, and LBM index in one view.

Calculator

Units & Profile

Units
Gender
Male Female
Age years

Height & Weight (Metric)

Height cm
Weight kg
Results update automatically
Results update live as you type
Status:Avg LBM 55.1 kg (121.5 lbs)78.7% lean · within the typical healthy rangeFat 21.3%

Lean Body Mass Summary

Average LBM55.1 kg (121.5 lbs)
Body Fat21.3%
Fat Mass14.9 kg (32.8 lbs)
LBM Index18.0 kg/m²
Lean Share78.7%

Composition Progress

Lean Mass55.1 kg / 70.0 kg
Fat Mass14.9 kg
LBMI Position18.0 kg/m²

Formula Breakdown

FormulaLBMBody Fat
Boer56.0 kg (123.5 lbs)20.0%
James56.5 kg (124.6 lbs)19.3%
Hume52.8 kg (116.4 lbs)24.6%
Average55.1 kg (121.5 lbs)21.3%

Results

Optimal

Average LBM

55.1 kg (121.5 lbs)

Mean of Boer, James, and Hume

Boer LBM

56.0 kg (123.5 lbs)

Boer 1984 — best all-round estimator

James LBM

56.5 kg (124.6 lbs)

James — steeper overweight penalty

Hume LBM

52.8 kg (116.4 lbs)

Hume 1966 clinical estimator

Body Fat (from avg)

21.3%

Fat mass 14.9 kg from average LBM

Fat Mass

14.9 kg (32.8 lbs)

Weight minus average LBM

LBM Index

18.0 kg/m²

Average LBM ÷ height² — BMI for lean tissue

LBM Share

78.7%

within the typical healthy range

LBM values average three population equations from height, weight, and sex. They track trends well but cannot replace DEXA, hydrostatic, or supervised BIA for drug dosing, sarcopenia diagnosis, or contest prep.

Visualizations

LBM by Formula

56 kgBoer
56.5 kgJames
52.8 kgHume

Composition Split (avg)

Lean mass79%
Fat mass21%

Lean Share of Weight

LBM78.7%

Lean vs Total Weight

LBM55.1 kg

Formula

Three population regressions estimate lean tissue from the same three inputs. Averaging them cancels each formula's cohort bias.

Boer M: 0.407W + 0.267H − 19.2 · F: 0.252W + 0.473H − 48.3

Alternative Form

James M: 1.1W − 128(W/H)² · F: 1.07W − 148(W/H)² — Hume M: 0.32810W + 0.33929H − 29.5336 · F: 0.29569W + 0.41813H − 43.2933 (W kg, H cm)

Variables

SymbolNameUnitDescription
WBody weightkgTotal scale weight
HHeightcmStanding height in centimetres
eLBMEstimated LBMkgBoer / James / Hume output
avgAverage LBMkgMean of the three estimates
BFPBody-fat %%(W − avg) ÷ W × 100
LBMILBM indexkg/m²avg ÷ height(m)²
shareLBM share%avg ÷ W × 100

Explanation

Each formula fits lean tissue against weight and height in its own cohort, so each carries that cohort's bias. Boer generalises best, James punishes high W/H hardest, Hume reflects 1960s clinical data — the mean behaves better than any single line across builds.

Derivation

Male 70 kg, 175 cm: Boer = 0.407×70 + 0.267×175 − 19.2 = 56.0 kg; James = 77 − 128×(0.4)² = 56.5 kg; Hume = 22.97 + 59.38 − 29.53 = 52.8 kg; avg ≈ 55.1 kg; BFP = (70 − 55.1)/70 = 21.3%.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Apply the Boer equation for weight, height, and sex.

eLBM = 0.407W + 0.267H − 19.2
Weight:70.0 kg
Height:175.0 cm
Gender:male
Intermediate: Population regression on W and H
Result: Boer = 56.0 kg (123.5 lbs)
Step 2

Apply the James equation with its quadratic penalty.

eLBM = 1.1W − 128(W/H)²
Weight:70.0 kg
Height:175.0 cm
Intermediate: (W/H)² = 0.1600
Result: James = 56.5 kg (124.6 lbs)
Step 3

Apply the Hume equation from clinical data.

eLBM = 0.32810W + 0.33929H − 29.5336
Weight:70.0 kg
Height:175.0 cm
Intermediate: Linear clinical fit
Result: Hume = 52.8 kg (116.4 lbs)
Step 4

Average the three to stabilise individual error.

Avg = (Boer + James + Hume) ÷ 3
Boer:56.0 kg
James:56.5 kg
Hume:52.8 kg
Intermediate: (56.0 + 56.5 + 52.8) ÷ 3
Result: Average LBM = 55.1 kg (121.5 lbs)
Step 5

Subtract from weight for fat mass and percentage.

Fat = W − avg; BFP = fat ÷ W × 100
Weight:70.0 kg
Avg LBM:55.1 kg
Intermediate: 70.0 − 55.1 = 14.9
Result: Fat 14.9 kg · 21.3% body fat
Step 6

Index lean tissue to height and grade the share.

LBMI = avg ÷ h²; share = avg ÷ W × 100
Height²:3.0625 m²
Share:78.7%
Intermediate: 55.1 ÷ 3.0625
Result: LBMI 18.0 kg/m² — within the typical healthy range
Final Answer
55.1 kg (121.5 lbs)

Worked Examples

See how the calculator works with different scenarios.

Scenario

A 30-year-old man, 175 cm, 70 kg.

Inputs

Height:175 cm
Weight:70 kg
Gender:Male

Calculation

Boer 56.0 · James 56.5 · Hume 52.8 Avg = (56.0 + 56.5 + 52.8) ÷ 3 = 55.1 kg

Result

Avg LBM 55.1 kg (121.5 lbs) · 21.3% body fat

Interpretation

Textbook reference build. LBM share ~79% sits comfortably inside the male 60-90% band — maintenance training and protein hold it there.

Understanding Your Result

Your Result: Average LBM: 55.1 kg (121.5 lbs)

Typical range: LBM share 60-90% men / 50-85% women; athletic 80-90% / 75-85%. LBMI roughly 16-20 men / 12-16 women. BFP health caps ~24% men / ~31% women.

What This Means

Three classic equations turn the same height and weight into three lean-mass guesses; the average is the headline, with fat mass, body-fat percentage, LBMI, and lean share derived from it.

Why It Matters

Scale weight hides composition. Two 85-kg men can differ by 15 kg of muscle — with different metabolisms, strength, drug handling, and risk. LBM exposes which kilograms work for you.

Professional Interpretation

Lead with the average and its BFP; cite Boer when one number is demanded (anaesthesia, renal estimates). Confirm consequential calls — dosing, sarcopenia, contest prep — with DEXA or supervised BIA.

Recommendations

  • •Track the average, not your favourite formula
  • •Lift 2-3× weekly with 1.6-2.2 g/kg protein to grow or keep LBM
  • •Cut on ≤750 kcal deficits to protect lean tissue
  • •Re-measure hydrated, same time of day
  • •Confirm dosing and sarcopenia calls with direct measurement

Educational Content

Introduction

The Lean Body Mass Calculator splits scale weight into working tissue and stored fat using three validated equations, then indexes the result to height for tracking.

Concept Explanation

eLBM regressions predict lean tissue from weight, height, and sex. Fat = weight − eLBM; BFP = fat ÷ weight; LBMI = eLBM ÷ height²; averaging three fits beats any single cohort fit.

Applications

▸Splitting weight into lean vs fat without a scan
▸Comparing Boer, James, and Hume behaviour on your build
▸Setting protein and calorie targets from lean mass
▸Screening sarcopenia and low-muscle risk
▸Informing weight-based drug and renal estimates
▸Tracking recomposition independent of scale weight

Benefits

  • •Three formulas averaged for stability
  • •Instant BFP, fat mass, LBMI, and lean share
  • •Composition bar makes lean-vs-fat obvious
  • •Works in metric and US units
  • •Flags healthy-band position automatically

Limitations

  • •Equations assume average density and hydration
  • •Weak for extreme muscle, pregnancy, or oedema
  • •Adult cohorts — not for young children
  • •Estimate, not a DEXA replacement for dosing

Best Practices

  • •Use morning, fasted, euhydrated weight
  • •Measure height barefoot to 0.5 cm
  • •Follow the average across time, not formula-hopping
  • •Pair with waist, strength, and photos for recomposition
  • •Confirm clinical decisions with direct measurement

Common Misconceptions

Myth: LBM and muscle mass are identical.
Truth: Muscle is the biggest slice of LBM, but bone, water, organs, and connective tissue count too.
Myth: One formula fits every build.
Truth: Each was fit to a different cohort. Heavy, light, and tall builds reorder them — hence the average.
Myth: More protein alone builds LBM.
Truth: Protein without progressive overload mostly burns off. Training is the signal; protein is the supply.
Myth: BIA and equations are equally wrong.
Truth: Both err, differently. Equations err by cohort; BIA errs by hydration. Standardise conditions and they track well together.

Practical Tips

  • •Weigh fasted and hydrated for comparability
  • •Record height barefoot each quarter
  • •Follow the average line over months
  • •Hit protein 1.6-2.2 g/kg across 3-4 meals
  • •Lift full-body 2-3× weekly with progression
  • •Screenshot the summary for training blocks
  • •Re-run after any 3-kg sustained change

Common Mistakes

Cherry-picking the highest formula
Report the average. Picking Boer because it flatters most hides the James warning on heavy builds.
Comparing dehydrated to hydrated readings
A litre of sweat swings LBM by ~1 kg on equations and more on BIA. Standardise fluid, food, and timing.
Cutting hard without lifting
Deficits over ~750 kcal plus no resistance training strip lean tissue. Keep the deficit moderate and keep the barbell.
Using child inputs on adult fits
Boer/James/Hume cohorts are adult. Under-13s need the Peters paediatric equation and clinical supervision.
Dosing drugs off an equation alone
Equations inform but do not replace weight, renal function, and pharmacist review — especially for chemo and anaesthesia.

Assumptions

This calculator makes the following assumptions to provide estimates:

Average Hydration: Assumes ~73% lean hydration; dehydration understates LBM and overstates fat.
Adult Cohorts: Fits derive from adult samples; accuracy falls for children and extreme elderly frailty.
Typical Density: Assumes average bone and muscle density; dense-boned or elite-muscular builds deviate.
Stable Inputs: One height-weight point; daily food, glycogen, and oedema noise are not modelled.

Limitations

Be aware of these limitations when using this calculator:

No Regional Split: Whole-body only — no limb/trunk breakdown like DEXA or segmental BIA.
Cohort Bias: Each formula inherits its era and sample; the average dampens but cannot erase that.
Extreme Builds: Bodybuilders, severe obesity, pregnancy, and oedema exceed the fitted ranges.
Not for Dosing Alone: Screening estimate only — anaesthetic, chemo, and renal dosing need direct review.

Frequently Asked Questions

Answers to common questions about this calculator.

What is lean body mass?
Total body weight minus all fat mass — bones, muscle, organs, skin, blood, and water. It is everything that is not stored fat.
What is the difference between LBM and muscle mass?
Muscle is the largest part of LBM but not all of it. LBM also includes bone, water, organs, and connective tissue.
What is the difference between LBM and fat free mass?
Fat-free mass excludes even essential organ fat; LBM includes it. FFM runs ~2-3% lower in men and ~5-12% lower in women.
How do you calculate lean body mass?
With Boer, James, or Hume equations from height, weight, and sex — or directly with DEXA, BIA, hydrostatic weighing, or Bod Pod. This page averages all three equations.
What is the Boer formula for LBM?
Men: 0.407W + 0.267H − 19.2. Women: 0.252W + 0.473H − 48.3, with W in kg and H in cm. Generally the best all-round estimator.
What is the James formula for LBM?
Men: 1.1W − 128(W/H)². Women: 1.07W − 148(W/H)². It penalises high weight-for-height more steeply, which can suit overweight builds.
What is the Hume formula for LBM?
Men: 0.32810W + 0.33929H − 29.5336. Women: 0.29569W + 0.41813H − 43.2933. A classic clinical estimator still used in renal and drug work.
Which LBM formula is most accurate?
Boer for most adults; James can edge it in overweight groups. Averaging all three — as here — beats trusting any single line.
What is LBM index (LBMI)?
LBM ÷ height² in kg/m² — BMI for lean tissue only. Useful for tracking recomposition independent of fat change.
What is a healthy LBM percentage?
Men 60-90% (athletic 80-90%); women 50-85% (athletic 75-85%). Below 60/50% suggests low muscle or high fat.
How does LBM differ between men and women?
Men carry ~5-15% more LBM at the same size from testosterone, muscle, and bone density; women carry more essential fat.
What is a typical LBM for athletes?
Male strength athletes 80-90%, females 75-85%. Endurance athletes sit slightly lower from lighter upper bodies.
What is a healthy LBM for seniors?
As high as possible — below 60% (men) or 50% (women) flags sarcopenia risk. Lift 2-3× weekly with 1.6-2.2 g/kg protein.
How can I increase my lean body mass?
Progressive resistance training, 1.6-2.2 g/kg protein spread over 3-4 meals, a 300-500 kcal surplus, and 7-9 hours of sleep.
How do I preserve LBM during weight loss?
Keep the deficit moderate (500-750 kcal), protein high, and keep lifting. Crash diets sacrifice roughly 1 lb of lean per 3-4 lbs lost.
Does protein intake increase LBM?
Protein supplies the bricks, but only training lays them. Without overload, extra protein mostly oxidises — with it, 20-40 g per meal maximises synthesis.
Does exercise increase LBM?
Resistance work does reliably; steady cardio barely moves LBM. Two to three full-body sessions weekly is the minimum effective dose.
Does age decrease LBM?
Yes — 3-8% per decade after 30, faster past 60. Sarcopenia is the clinical term, and lifting plus protein slows or reverses it at any age.
What is sarcopenia?
Age-related loss of muscle mass, strength, and function — raising fall, fracture, and mortality risk. Grip strength and gait speed screen for it.
How does LBM affect metabolism?
LBM drives 60-75% of daily burn. Each pound of muscle uses ~6-10 kcal/day at rest, so more LBM means a higher maintenance budget.
What is the relationship between LBM and BMR?
Nearly linear: BMR rises with lean tissue. Katch-McArdle (BMR = 370 + 21.6 × LBM) makes the link explicit.
How does LBM affect insulin sensitivity?
Muscle is the main glucose sink. More LBM clears blood sugar faster, lowering diabetes risk independent of fat loss.
How can I measure LBM at home?
BIA scales or calipers for trends, or this calculator for an instant estimate. Standardise hydration, timing, and device for comparability.
Why is LBM important for health?
It governs strength, glucose control, bone density, drug handling, and survival — low LBM predicts frailty and mortality in seniors.
How does hydration affect LBM measurements?
Muscle is ~75% water, so dehydration understates LBM and overstates fat — especially on BIA. Measure euhydrated, same time of day.
Can you lose LBM too fast?
Yes — very-low-calorie diets and cardio-only cuts strip muscle. Losing over 1% of body weight weekly without lifting is the red flag.
What is the relationship between LBM and bone density?
Heavier muscles tug harder on bone, stimulating formation. Higher LBM tracks with higher mineral density and fewer fractures.
How does LBM affect longevity?
Preserved LBM predicts survival, independence, and fewer hospitalisations in older age — strength is a longevity vital sign.
Which drugs are dosed based on LBM?
Propofol, thiopental, carboplatin, aminoglycosides, vancomycin, succinylcholine, and rocuronium — hydrophilic drugs that distribute in lean tissue.
Why is LBM important for surgery?
It guides anaesthetic dosing, clearance estimates, and nutrition risk. Low preoperative LBM predicts complications and slower recovery.
How is LBM used for creatinine clearance?
Cockcroft-Gault with LBM or ideal weight avoids overestimating kidney function in obesity, keeping renally cleared drugs safe.
What is the DEXA scan and how does it measure LBM?
Dual-energy X-ray absorptiometry separates bone, lean, and fat pixel by pixel — the research gold standard with regional breakdowns.
How accurate are BIA scales for measuring LBM?
Within ~3-5% of DEXA when hydrated, fasted, and rested — but food, sweat, and alcohol swing readings by several points.
Can LBM be too high?
In natural lifters, rarely a health problem. Extreme drug-driven mass can strain the heart — context and blood pressure decide.
Does LBM affect athletic performance?
Decisively for strength and power; for endurance, the LBM-to-weight ratio matters more than absolute mass.

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Related Guides

Deepen your understanding with these educational resources.

Glossary

Technical terms used in mortgage calculations explained in plain language.

Lean body mass (LBM)
Weight minus all fat mass: muscle, bone, water, organs, skin, and connective tissue.
Fat-free mass (FFM)
Weight minus all fat including essential organ fat — slightly below LBM.
Boer formula
1984 weight-height regression; the best general-purpose eLBM estimator.
James formula
Weight-height estimator with a quadratic overweight penalty.
Hume formula
1966 clinical weight-height estimator for lean tissue.
Body-fat percentage
(Weight − LBM) ÷ weight × 100 from the averaged LBM.
LBMI
LBM ÷ height² — lean-only analogue of BMI for tracking recomposition.
Sarcopenia
Age-related loss of muscle mass, strength, and function.
DEXA
Dual-energy X-ray absorptiometry — gold-standard body-composition imaging.
BIA
Bioelectrical impedance analysis — scale-based estimate sensitive to hydration.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

Boer / James / Hume peer-reviewed eLBM equationsDEXA as reference method for body composition

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Page Information

Last Updated:

2026-09-14

Version:

2.0.0

License:

Free to use for educational and professional purposes.