Lean Body Mass Calculator

Lean Body Mass (LBM) is your total body weight minus all fat mass. It includes muscle, bone, organs, and water.

From Body Fat Percentage: Fat Mass = Weight × (Body Fat % / 100) Lean Body Mass = Weight - Fat Mass

If body fat % is unknown, use the Boer Formula:

For Males: LBM (kg) = 0.407 × weight(kg) + 0.267 × height(cm) - 19.2

For Females: LBM (kg) = 0.252 × weight(kg) + 0.473 × height(cm) - 48.3

Typical body fat ranges:

Why LBM matters:

• Medication dosing: Some drugs are dosed based on lean mass
• Fitness goals: Track muscle gain separate from fat loss
• Metabolic rate: LBM is the primary driver of basal metabolism
• Body composition: A better health indicator than weight alone

Unit conversions:

• 1 kg = 2.205 lbs | 1 lb = 0.4536 kg
• 1 cm = 0.394 in | 1 in = 2.54 cm

LBM and FFM are not exactly the same. The terms get used interchangeably, but they are slightly different. Fat-Free Mass (FFM) excludes all fat. Lean Body Mass (LBM) includes the small amount of essential fat needed for organ and hormonal function (roughly 3% in men, 12% in women). The numerical gap is small, but in clinical settings where dosing matters, the distinction can shift a prescription by a meaningful amount.

Sarcopenia — lean mass declines with age. Without resistance training, adults lose roughly 3-8% of muscle mass per decade after age 30, and the rate accelerates after 60. Two people of identical weight and height but different ages can have substantially different LBM values. This is why LBM-based drug dosing tends to be more accurate than weight-based dosing for elderly patients, and why strength training matters more as you age than most cardio.