Lean Body Mass Calculator

What Is Lean Body Mass?

Lean body mass (LBM) is everything in your body that is not fat. This includes skeletal muscle, bone, organs, blood, water, and connective tissue. When people talk about "gaining lean mass" or "preserving muscle," they are really talking about this number.

LBM is arguably a more useful metric than total body weight because it tells you what your body is made of, not just how much it weighs. Two people can stand on a scale at the same weight and have dramatically different physiques — one carrying significantly more muscle and less fat than the other. Tracking lean body mass helps you see whether you are actually gaining muscle, losing fat, or both.

Understanding your LBM is also essential for setting accurate nutrition targets. Many evidence-based protein recommendations are calculated relative to lean mass rather than total body weight, which provides a more precise target — especially for those who are significantly overweight.

How Is It Calculated?

The simplest way to estimate lean body mass is to subtract your fat mass from your total weight:

LBM = Total Body Weight × (1 − Body Fat % / 100)

This calculator uses the Boer formula, which estimates LBM directly from height and weight without requiring a body fat measurement:

• Men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2
• Women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3

The Boer formula is considered one of the more accurate prediction equations for lean mass estimation. For even greater accuracy, DEXA scans or hydrostatic weighing can measure body composition directly.

Why LBM Matters for Your Metabolism

Your basal metabolic rate — the number of calories your body burns at rest — is primarily determined by how much lean mass you carry. Muscle tissue is metabolically active; it requires energy to maintain even while you are sleeping. The more lean mass you have, the more calories you burn around the clock. This is one of the key reasons that resistance training is so valuable during a fat-loss phase: it helps you hold onto the muscle that keeps your metabolism elevated.

How to Increase Your Lean Body Mass

• Resistance training: Lifting weights or performing bodyweight exercises that challenge your muscles is the single most effective way to build lean mass. Focus on compound movements like squats, deadlifts, bench press, and rows.
• Adequate protein: Consume at least 0.7–1.0 g of protein per pound of body weight daily to provide the amino acids your muscles need to grow and repair.
• Progressive overload: Gradually increase the weight, reps, or sets over time. Your muscles adapt to the demands placed on them, so the stimulus must keep increasing to drive growth.
• Sufficient calories: Building muscle requires energy. A modest calorie surplus of 200–400 calories above maintenance supports muscle growth while limiting excess fat gain.
• Sleep and recovery: Muscle repair and growth hormone release peak during deep sleep. Aim for seven to nine hours per night.

Tracking Body Composition Over Time

Instead of relying solely on the bathroom scale, re-estimate your lean body mass every four to eight weeks. If your weight stays the same but your LBM goes up, you are successfully building muscle while losing fat — a process called body recomposition. Progress photos, tape measurements, and how your clothes fit are also useful indicators alongside the numbers.

Related Calculators

Estimate your fat-to-lean ratio with the Body Fat Calculator, dial in your daily protein target with the Protein Calculator, or find your full daily calorie needs with the TDEE Calculator.