Lean Body Mass (LBM) Calculator
Estimate your lean body mass (fat-free mass) from weight, height, and optional body fat %. Boer, James, and Hume formulas, fat mass breakdown, LBM percentage, daily protein target (1.6–2.2 g/kg), and PDF export.
Enter your details — results appear below after you calculate.
Body measurements
Allowed range: 30–300 kg
Allowed range: 120–230 cm
Allowed range: 3–60%. If known, enter body fat % for a direct LBM calculation. Use our Body Fat Calculator to estimate it.
How this Lean Body Mass (LBM) Calculator works
Enter your sex, weight, and height (metric or imperial). Optionally add body fat % from DEXA, calipers, or bioimpedance for a direct LBM calculation: weight × (1 − body fat %). Without body fat %, we use the Boer (1984) formula as the default estimate and show James (1976) and Hume (1966) for comparison.
Your report includes lean body mass (kg), fat mass (kg), LBM as % of total weight, a three-formula comparison table with estimated body fat % per formula, and a protein target of 1.6–2.2 g per kg of LBM. LBM is fat-free mass (muscle, bone, organs, water)—not muscle alone. Export a PDF or share results for nutrition planning.
Lean mass also feeds the Katch-McArdle BMR equation (370 + 21.6 × LBM kg) used in our BMR and TDEE calculators when body fat % is known. Re-run every 4–8 weeks during fat loss or muscle-building phases to track composition trends.
For deeper composition and calorie planning, pair with our Body Fat Calculator, Protein Target Calculator, and TDEE Calculator.
Lean Body Mass (LBM) Calculator — Fat-Free Mass & Protein Target
Our free lean body mass calculator—also called a fat-free mass calculator or muscle mass calculator—estimates your fat-free mass (FFM) from weight, height, sex, and optional body fat percentage. Whether you need LBM for protein planning, Katch-McArdle BMR, or body recomposition tracking, this tool delivers lean body mass (kg), fat mass (kg), LBM as % of total weight, side-by-side results from three published formulas (Boer, James, Hume) with estimated body fat %, and a daily protein target of 1.6–2.2 g per kg of LBM. Works in metric (kg, cm) or imperial (lb, in) with PDF export.
How to Use This Lean Body Mass Calculator
- Select sex (male or female) and units (metric or imperial).
- Enter weight and height—the core inputs for all height-weight LBM formulas.
- Optionally enter body fat % if you know it from DEXA, skinfold calipers, or bioimpedance (BIA). This switches to the direct LBM formula for higher accuracy.
- Tap "Calculate lean body mass" to see LBM, fat mass, LBM %, formula comparison table, and protein target range.
- Export or share your PDF report, or cross-link to our Body Fat, Protein Target, and TDEE calculators.
What Results You Get
- Lean body mass (kg) — estimated fat-free mass using Boer (default) or body fat % when provided
- Fat mass (kg) — total body fat (weight minus LBM)
- LBM as % of total body weight — (LBM ÷ weight) × 100
- Results from 3 formulas — Boer (1984), James (1976), and Hume (1966) side-by-side with LBM, fat mass, LBM %, and body fat %
- Protein target — recommended daily intake of 1.6–2.2 g protein per kg of LBM
- Interpretation & recommendations — plain-language summary and next steps
- PDF export and share — save or send your full report
What Is Lean Body Mass?
Lean body mass (LBM), also called fat-free mass (FFM), is everything in your body except stored adipose (fat) tissue—skeletal muscle, bone, organs, blood, connective tissue, and water. Unlike BMI, which only uses height and weight, LBM reflects body composition and is central to nutrition science, sports performance, and metabolic health.
LBM is not the same as muscle mass alone—muscle is the largest component, but bone and organ weight are included. For everyday fitness and protein planning, LBM is a practical proxy for metabolically active tissue.
This calculator is an educational tool. For clinical body-composition testing, DEXA, BIA, or hydrostatic weighing provide more accurate measurements. Pair results with our Body Fat Calculator, Protein Target Calculator, and TDEE Calculator.
1What You Enter
Required inputs
- Sex — male or female (all LBM formulas use sex-specific coefficients)
- Weight — total body weight in kg or lb (morning, after bathroom, light clothing for consistency)
- Height — standing height in cm or inches without shoes
Optional input & tips
- Body fat % — from DEXA, skinfold calipers, or bioimpedance (BIA). Switches to the direct LBM formula for higher accuracy.
- Weigh yourself at the same time of day for comparable results
- If body fat % is unknown, use our Body Fat Calculator first, then re-run with that value
- Re-calculate every 4–8 weeks during fat loss or hypertrophy blocks
2LBM Calculation Formulas
When body fat % is not provided, we use three published height-weight formulas. Boer (1984) is the default. W = weight in kg, H = height in cm.
Boer Formula (1984) — Default
Male: LBM = 0.407 × W + 0.267 × H − 19.2
Female: LBM = 0.252 × W + 0.473 × H − 48.3
James Formula (1976)
Male: LBM = 1.1 × W − 128 × (W/H)²
Female: LBM = 1.07 × W − 148 × (W/H)²
Hume Formula (1966)
Male: LBM = 0.32810 × W + 0.33929 × H − 29.5336
Female: LBM = 0.29569 × W + 0.41813 × H − 43.2933
Body Fat % Route (when provided)
LBM = W × (1 − body fat % ÷ 100)
Fat mass = W − LBM
LBM % = (LBM ÷ W) × 100
3Protein Target from LBM
Research on resistance-trained adults supports 1.6–2.2 g of protein per kg of lean body mass daily for muscle protein synthesis and preservation during fat loss. This calculator multiplies your estimated LBM by 1.6 and 2.2 to show the range.
Example: 65 kg LBM → 104–143 g protein/day. For sedentary individuals or specific goals (GLP-1, elderly), use our Protein Target Calculator for tailored recommendations.
4How Fat Mass & Body Fat % Are Derived
Fat mass
Fat mass (kg) = Total weight − Lean body mass
Once LBM is estimated (Boer default, body fat % direct, or comparison formulas), fat mass is simply what remains of total weight.
LBM %
LBM % = (LBM ÷ Total weight) × 100
Body fat % (from formulas)
Body fat % = (Fat mass ÷ Total weight) × 100 = 100 − LBM %
In the three-formula comparison table, each row shows its own estimated body fat % derived from that formula's LBM—not your measured body fat % unless you entered it.
5Worked Examples
Example 1 — Male, Boer formula
Inputs: Male, 80 kg, 178 cm, no body fat %
Boer: LBM = 0.407×80 + 0.267×178 − 19.2 = 63.4 kg
Fat mass = 80 − 63.4 = 16.6 kg
LBM % = 79.3% · Body fat % ≈ 20.7%
Protein target: 101–139 g/day
Example 2 — Female, body fat % direct
Inputs: Female, 62 kg, 165 cm, 25% body fat
Direct: LBM = 62 × (1 − 0.25) = 46.5 kg
Fat mass = 62 − 46.5 = 15.5 kg
LBM % = 75% · Body fat % = 25%
Protein target: 74–102 g/day
6LBM & Katch-McArdle BMR
Lean body mass powers the Katch-McArdle basal metabolic rate (BMR) equation—often more accurate than height-weight formulas when body composition is known:
BMR = 370 + (21.6 × lean body mass in kg)
Example: 65 kg LBM → BMR ≈ 1,774 kcal/day before activity. Multiply BMR by an activity factor for TDEE. Our BMR Calculator and TDEE Calculator accept body fat % to derive lean mass automatically for this formula.
Typical LBM % Ranges (Approximate)
LBM as a percentage of total weight varies by sex, age, and training status. These are general population ranges—not diagnostic cutoffs:
| Group | Typical LBM % | Notes |
|---|---|---|
| Men, average fitness | 75–85% | Higher muscle and bone mass vs women at similar BMI |
| Women, average fitness | 65–75% | Essential fat requirements are higher for women |
| Athletic / lean | 80–90%+ (men), 70–80%+ (women) | Resistance training and low body fat raise LBM % |
| Higher body fat | Below ~70% | James formula may track better than Boer at high BMI |
Boer vs James vs Hume — Which to Trust?
| Formula | Year | Best for | Notes |
|---|---|---|---|
| Boer | 1984 | Default; normal BMI adults | Most cited in clinical guidelines; our primary when BF% unknown |
| James | 1976 | Obesity; anaesthetic dosing | (W/H)² correction; may track better at high BMI |
| Hume | 1966 | Literature comparison | Older formula; useful for research cross-checks |
| Body fat % direct | — | When BF% is known | Most accurate route when body fat % is measured |
Studies comparing height-weight formulas to DEXA show agreement within roughly ±5–12 kg depending on population and BMI. Estimates between formulas can differ by several kilograms—use them for education and tracking trends, not clinical dosing.
Using LBM for Different Fitness Goals
Fat loss
Aim to preserve lean mass while reducing fat mass. Protein at 1.6–2.2 g/kg LBM plus resistance training helps minimize muscle loss. Track LBM monthly—if estimated LBM drops sharply, calories or protein may be too low.
Muscle gain
Use LBM-based protein targets and a slight calorie surplus from our TDEE Calculator. Rising LBM with stable or slowly rising weight suggests successful hypertrophy; pair with progressive overload in the gym.
Maintenance & health
Knowing LBM helps set realistic protein and calorie needs beyond generic per-kg-total-weight rules. Combine with BMI and body fat % for a fuller composition picture—not weight on the scale alone.
Common Mistakes When Estimating LBM
1. Using total body weight for protein
Protein needs scale with lean mass, not fat mass. A 100 kg person at 30% body fat has far less metabolically active tissue than a 100 kg person at 12% body fat—LBM-based targets (1.6–2.2 g/kg) are more appropriate for athletes.
2. Ignoring body fat % when available
Height-weight formulas are population averages. If you have DEXA, caliper, or BIA body fat %, always enter it—the direct formula is more personalized than Boer, James, or Hume alone.
3. Treating LBM as pure muscle mass
LBM includes bone, organs, blood, and water. A 5 kg LBM increase over months does not mean 5 kg of new muscle—some is glycogen, water, and connective tissue.
4. Expecting formula precision
Boer, James, and Hume can disagree by several kg. Use them for trends and education over time—not single-point clinical dosing. Re-measure with consistent inputs every 4–8 weeks.
How to Track Lean Body Mass Over Time
- Baseline: Calculate LBM with the same method (ideally with measured body fat %) at the start of a program.
- Consistent inputs: Weigh at the same time of day, same scale, same hydration state when possible.
- Re-test every 4–8 weeks: Compare Boer LBM or direct LBM trends—not day-to-day fluctuations.
- Cross-check: Pair with waist circumference, progress photos, strength gains, and our Body Fat Calculator for validation.
- Export PDFs: Save reports from this calculator to compare formula results and protein targets across check-ins.
Who Should Use This Calculator?
- Fitness enthusiasts tracking body recomposition during fat loss or muscle gain
- Strength athletes setting protein targets based on lean mass rather than total weight
- Anyone curious about fat-free mass vs total body weight
- People using Katch-McArdle BMR who want to understand their lean-mass input
- Nutrition planners cross-checking LBM before using our Protein Target or TDEE tools
Not intended for chemotherapy dosing, anaesthetic drug calculations, or replacing DEXA/BIA clinical testing.
LBM vs Other Body Composition Metrics
LBM complements—not replaces—other metrics. Use multiple tools for a complete picture:
| Metric | What it measures | LBM calculator relation |
|---|---|---|
| BMI | Weight ÷ height² categories | Ignores muscle vs fat; LBM adds composition context |
| Body fat % | Proportion of weight as fat | Enter BF% here for direct LBM; or estimate via our Body Fat Calculator |
| Waist / WHR | Central fat distribution | LBM does not show where fat is stored—pair with WHR tools |
| BMR / TDEE | Daily energy expenditure | Katch-McArdle BMR uses LBM; feed this tool's output into calorie planning |
Related Tools on This Site
Pair this calculator with our Body Fat Percentage Calculator to estimate body fat % if unknown, Protein Target Calculator for goal-specific daily protein grams, and TDEE Calculator for daily calorie needs. For metabolism depth, try our BMR Calculator (Katch-McArdle uses lean mass) and BMI Calculator.
Frequently Asked Questions (FAQs)
Related Calculators
You might also be interested in these related health and wellness calculators:
Macronutrient & Calorie Calculator
Calculate your daily calorie needs and get a personalized macronutrient split (protein, carbs, fats) based on your body stats, activity level, and health goal. Perfect for fat loss, muscle gain, or maintenance.
Body Fat Percentage Calculator
Calculate your body fat to understand your fitness level and monitor changes over time more accurately than just weighing yourself.
Body Mass Index (BMI) Calculator
Calculate your Body Mass Index (BMI) from height and weight in metric or imperial units. Get WHO categories, healthy weight range, BMI Prime, and PDF export.
Ideal Body Weight Calculator
Calculate ideal weight for your height using Devine, Robinson, Miller, and Hamwi formulas. See average, ideal weight range, frame-size adjustment, and current-weight comparison.
Protein Target Calculator
Calculate daily protein targets in grams from body weight, goal, and training—with GLP-1 muscle-preservation (1.6–2.2 g/kg), adjusted weight above 100 kg, sedentary 0.8–1.2 g/kg, and per-meal splits.
Basal Metabolic Rate (BMR) Calculator
Estimate your basal metabolic rate (BMR)—resting calorie burn—from your body stats. Optional body fat % for a personalized estimate. See activity-based daily calorie estimates.
Total Daily Energy Expenditure (TDEE) Calculator
Calculate your Total Daily Energy Expenditure (TDEE) and BMR using a validated metabolic formula. Select your goal (lose weight, maintain, gain muscle) for ±500 kcal targets and macro split suggestions.
Healthy Weight Gain & Muscle Building Calculator
Calculate your daily calorie surplus and target for healthy weight gain from body stats, activity, goal weight, goal type, and timeline. See TDEE, macro split, weekly gain rate, goal date, and safety warnings.