Lean Body Mass Calculator
Calculate your lean body mass using 4 formulas. Get a body composition breakdown, LBM-based goals, and protein needs based on your lean mass.
58.0 kg
LEAN MASS
17.0 kg
FAT MASS
22.6%
BODY FAT %
Body Measurements
Lean Body Mass (Boer)
58.0 kg
22.6% estimated body fat · 17.0 kg fat mass
58.0 kg
LBM (Boer)
17.0 kg
Fat Mass
22.6%
Body Fat %
24.5
BMI
🧮 Composition
📐 Formula Comparison
58.0 kg
Boer
59.0 kg
James
54.5 kg
Hume
56.0 kg
Peters (children)
🎯 Goal & Protein
To reach 15% body fat while keeping your current lean mass, your target weight is 68.3 kg.
Recommended daily protein: 93–128g (1.6–2.2g per kg of lean mass).
What is Lean Body Mass?
Lean Body Mass (LBM) is the weight of everything in your body except fat — muscle, bone, organs, water, and connective tissue. It's a more meaningful health metric than total body weight because it separates the “useful” mass (muscle, bone) from stored fat. LBM is used in medicine to calculate drug dosages, determine protein requirements, set fitness goals, and monitor body composition changes over time. Athletes track LBM to confirm they're building muscle and losing fat at the same time. For the body-fat-percentage input some LBM context comes from, see our body fat calculator, and for a BMR formula that uses lean mass directly, see our BMR calculator.
🧮 The Four LBM Formulas
Boer (1984) — Male: LBM = 0.407W + 0.267H − 19.2 | Female: LBM = 0.252W + 0.473H − 48.3James (1976) — Male: LBM = 1.10W − 128(W/H)² | Female: LBM = 1.07W − 148(W/H)²Hume (1966) — Male: LBM = 0.3281W + 0.3393H − 29.5336 | Female: LBM = 0.2969W + 0.4135H − 43.2933Peters (children) — LBM = 3.8 × (0.0215 × W^0.6469 × H^0.7236)W = weight in kg, H = height in cm.
🤔 Which Formula Should I Use?
The Boer formula is considered the most accurate for average-weight adults and is the most commonly used in clinical settings. The James formula can underestimate LBM in obese individuals. The Hume formula performs well across a wide range of body types. The Peters formula is specifically designed for children and adolescents under 14.
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Resistance Training
Progressive overload with weights is the most effective way to increase skeletal muscle mass and therefore LBM.
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Protein Intake
Consume 1.6-2.2g of protein per kg of LBM daily. Spread intake across meals for optimal muscle protein synthesis.
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Sleep & Recovery
Muscle repair and growth primarily occur during sleep. Aim for 7-9 hours. Poor sleep elevates cortisol and impairs gains.
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Track Trends
LBM is more meaningful than scale weight. If weight stays flat but LBM rises, you're gaining muscle and losing fat — a great outcome.
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