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Body Composition

Lean Body Mass Calculator

Calculate your lean body mass — everything that isn't fat: muscle, bone, organs, and water.

Lean Body Mass Calculator

Boer · James · Hume formulas

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Lean Body Mass (kg)

Lean Body Mass (LBM) is total body weight minus fat mass. It's a key metric for dosing medications, calculating protein targets, and measuring true training adaptations. Unlike scale weight, improvements in LBM mean you're gaining muscle or bone density.

Uses the Boer formula (most widely validated): Men: 0.407W + 0.267H − 19.2. Women: 0.252W + 0.473H − 48.3.

Estimated Lean Body Mass by Height & Body Fat %

Body WeightBody Fat %LBM (kg)LBM (lbs)
70 kg / 154 lbs15%59.5 kg131 lbs
80 kg / 176 lbs15%68 kg150 lbs
90 kg / 198 lbs20%72 kg159 lbs
100 kg / 220 lbs25%75 kg165 lbs
60 kg / 132 lbs25% (women)45 kg99 lbs

Why Lean Body Mass Matters for Athletes

Protein requirements are typically expressed per kg of lean body mass rather than total body weight. If you're 100 kg at 25% body fat, your LBM is 75 kg — and that's the number you should target for your 1.8–2.2 g/kg protein intake. LBM also drives resting metabolic rate — more muscle means more calories burned at rest. Tracking LBM over time is the best way to confirm that a bulk is producing actual muscle, not just fat.

LBM vs. Fat-Free Mass

LBM and Fat-Free Mass (FFM) are nearly identical but technically different. FFM excludes essential fat in the nervous system and organs; LBM may include some essential fat. For practical training purposes, the terms are interchangeable.

Frequently Asked Questions

Progressive resistance training (compound lifts 2–4x/week), high protein intake (1.6–2.2 g/kg LBM), and adequate sleep are the three pillars. A slight calorie surplus (~200–300 kcal) accelerates muscle gain without excessive fat storage.
There's no universal target — it depends on height, sex, and goals. The FFMI calculator can contextualize your LBM relative to height. Natural male athletes typically max out around FFMI 25–26.
Yes — this is called a body recomposition. It's most pronounced in beginners, those returning from a training break, or people with higher body fat levels. It requires high protein intake (2.0–2.4 g/kg), consistent resistance training, and a modest calorie deficit or at-maintenance calories. Progress is slower than dedicated bulk or cut phases but is sustainable long-term.
Lean body mass includes water, glycogen stores, bone density, and organ mass — not just muscle. Glycogen (stored carbohydrate in muscle) alone can account for 1–3 kg of fluctuation. This is why scale weight and LBM both fluctuate day-to-day even with no change in actual muscle tissue.

Related Calculators

FFMI CalculatorContext for your lean mass — are you maximizing your natural potential?Calculate FFMI → Body Fat % CalculatorKnow your fat percentage to better understand your LBM breakdown.Calculate Body Fat → Ideal Weight CalculatorSee what lean body composition looks like at your height.Calculate → Waist to Hip Ratio CalculatorAssess body fat distribution and cardiovascular risk.Calculate →