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Lean Body Mass Calculator

Fitness & Health

Calculate your lean body mass (LBM) — the weight of everything except body fat — using four medical formulas: Boer, James, Hume, and Katch-McArdle. Supports metric and US units. Enter body fat % for the most accurate Katch-McArdle result.

Explore This Tool in Context

Lean Body Mass Calculator is part of the Fitness & Health collection. If you want a broader view of similar workflows, open the Fitness & Health category page or browse all QuickTools categories.

Common next steps after this tool include BMI Calculator, Calorie Calculator and Body Fat Calculator.

How to Use the Lean Body Mass Calculator

  1. Select your unit system — choose Metric (cm / kg) or US (ft/in / lbs) using the toggle at the top of the calculator.
  2. Choose your gender — the Boer, James, and Hume formulas each use gender-specific coefficients, so this field is required.
  3. Enter your height and weight — these two fields are required. All inputs are validated to a sensible physiological range.
  4. Add body fat % (optional) — if you know your body fat percentage (from DEXA, hydrostatic weighing, or a skinfold test), entering it unlocks the most accurate Katch-McArdle formula and a full lean-vs-fat breakdown bar.
  5. Click Calculate LBM — instantly see your LBM from each formula, the average, your BMI, and (if body fat was entered) your fat mass and lean mass percentages.

How Lean Body Mass Is Calculated

Lean body mass (LBM) is the total body weight minus all stored fat. Because you cannot simply measure LBM without laboratory equipment, scientists have derived regression formulas from large datasets of measured body compositions. This calculator uses the four most widely validated formulas:

Boer (1984)Clinical standard

♂ Male: LBM = 0.407 × W + 0.267 × H − 19.2

♀ Female: LBM = 0.252 × W + 0.473 × H − 48.3

Most widely used in clinical and fitness settings. Derived from Dutch population data.

James (1949)Drug dosing

♂ Male: LBM = 1.1 × W − 128 × (W/H)²

♀ Female: LBM = 1.07 × W − 148 × (W/H)²

Originates from pharmacokinetic research. Standard for calculating medication doses in obese patients.

Hume (1966)Research

♂ Male: LBM = 0.3281 × W + 0.3393 × H − 29.534

♀ Female: LBM = 0.2957 × W + 0.4181 × H − 43.293

Derived from direct body composition measurements. Commonly cited in academic literature.

Katch-McArdleMost accurate (requires BF%)

♂ Male: LBM = W × (1 − BF% / 100)

♀ Female: LBM = W × (1 − BF% / 100)

Only applicable when body fat % is measured. Used in the most precise BMR/TDEE calculations. Gender-independent.

W = weight in kg  ·  H = height in cm  ·  BF% = body fat percentage

Worked Examples

Example 1 — Male, 175 cm, 80 kg (Metric, no body fat)

  1. 1.Boer: 0.407 × 80 + 0.267 × 175 − 19.2 = 32.56 + 46.72 − 19.2 = 60.1 kg
  2. 2.James: 1.1 × 80 − 128 × (80/175)² = 88 − 128 × 0.2089 = 88 − 26.7 = 61.3 kg
  3. 3.Hume: 0.3281 × 80 + 0.3393 × 175 − 29.534 = 26.2 + 59.4 − 29.5 = 56.1 kg
  4. 4.Average LBM: (60.1 + 61.3 + 56.1) / 3 = 59.2 kg

Example 2 — Female, 5’5″ (165.1 cm), 140 lbs (63.5 kg), BF 28%

  1. 1.Boer: 0.252 × 63.5 + 0.473 × 165.1 − 48.3 = 16.0 + 78.1 − 48.3 = 45.8 kg
  2. 2.James: 1.07 × 63.5 − 148 × (63.5/165.1)² = 67.9 − 148 × 0.1479 = 67.9 − 21.9 = 46.0 kg
  3. 3.Hume: 0.2957 × 63.5 + 0.4181 × 165.1 − 43.293 = 18.8 + 69.0 − 43.3 = 44.5 kg
  4. 4.Katch-McArdle: 63.5 × (1 − 0.28) = 63.5 × 0.72 = 45.7 kg
  5. 5.Average LBM (4 formulas): 45.5 kg · Fat mass: 63.5 − 45.5 = 18.0 kg (28%)

LBM Reference Chart (Boer Formula)

HeightWeightLBM ♂ MaleLBM ♀ Female
160 cm55 kg44.1 kg (97 lbs)37.2 kg (82 lbs)
165 cm60 kg48.7 kg (107 lbs)39.9 kg (88 lbs)
170 cm65 kg51.7 kg (114 lbs)41.5 kg (91 lbs)
170 cm70 kg53.8 kg (119 lbs)42.8 kg (94 lbs)
175 cm70 kg55.2 kg (122 lbs)44.7 kg (98 lbs)
175 cm80 kg59.3 kg (131 lbs)47.3 kg (104 lbs)
180 cm75 kg57.8 kg (127 lbs)47.2 kg (104 lbs)
180 cm90 kg63.9 kg (141 lbs)51.0 kg (112 lbs)
185 cm85 kg62.5 kg (138 lbs)50.1 kg (110 lbs)
185 cm100 kg68.6 kg (151 lbs)55.0 kg (121 lbs)

Why Lean Body Mass Matters

🔥Accurate BMR & TDEE

The Katch-McArdle formula calculates BMR directly from LBM, producing more accurate calorie targets than weight-based formulas for lean or muscular individuals.

💪Strength Benchmarks

Relative strength (e.g. 1-rep max ÷ LBM) is a better training metric than absolute strength, allowing fair comparison regardless of body weight.

💊Drug Dosing

Many medications (antibiotics, anaesthetics, chemotherapy) are dosed on LBM rather than total body weight to avoid overdosing obese patients.

📊Body Recomposition Tracking

When gaining muscle and losing fat simultaneously, total weight may stay constant. Tracking LBM over time confirms real body composition change.

⚡Faster Metabolism

Muscle tissue burns ∼6 kcal/kg/day at rest compared to ∼2 kcal/kg for fat. Higher LBM directly raises your resting metabolic rate (RMR).

📈Protein Target

Optimal protein intake (1.6–2.2 g/kg) for muscle growth or preservation is best applied to LBM, not total body weight, to avoid over-estimating needs.

Frequently Asked Questions

What is lean body mass?+

Lean body mass (LBM) is your total body weight minus all stored fat. It includes skeletal muscle, organs, bones, skin, connective tissue, and body water. Most adults have an LBM of 60–90% of their total body weight, depending on body fat percentage.

What is the difference between lean body mass and fat-free mass?+

The terms are often used interchangeably. Technically, fat-free mass (FFM) excludes all lipids including essential structural fat in cell membranes, whereas LBM includes a small amount of essential fat (≈3% in men, ≈12% in women). For practical fitness purposes the difference is negligible.

Which LBM formula is most accurate?+

When you know your body fat percentage (from DEXA, hydrostatic weighing, or an accurate skinfold test), the Katch-McArdle formula is the most accurate because it is directly derived from that measurement. Without body fat data, the Boer formula is generally considered the most reliable for the general adult population.

Can I increase my lean body mass?+

Yes. Progressive resistance training (weightlifting) combined with sufficient protein intake (1.6–2.2 g/kg of LBM/day) and a caloric surplus or maintenance is the most effective strategy. Beginners can gain 0.5–1 kg of lean mass per month; advanced trainees gain significantly less.

How do I use LBM to calculate my calorie needs?+

The Katch-McArdle formula calculates BMR as: BMR = 370 + (21.6 × LBM in kg). Multiply by your activity factor (1.2–1.9) to get TDEE. This is more accurate than weight-based formulas for people with above-average muscle or fat levels.

Does lean body mass decrease with age?+

Yes. Sarcopenia (age-related muscle loss) begins around age 30–35 and accelerates after 50, resulting in a loss of approximately 1–2% of muscle mass per year without resistance training. Maintaining LBM through strength training and adequate protein intake is one of the most important factors in healthy ageing.

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