How is lean body mass calculated?

Without body fat percentage data, LBM is estimated using regression formulas based on height and weight — the Boer, James, and Hume formulas. If you know your body fat percentage, a more accurate calculation is: LBM = total weight × (1 − body fat% ÷ 100). This calculator uses whichever method is available based on what you enter.

Why does lean body mass matter?

LBM determines your basal metabolic rate — the more lean mass you carry, the more calories you burn at rest. It is also used to set protein targets (most recommendations are per kg of LBM rather than total body weight), and it is a key metric for tracking whether you're gaining muscle, losing fat, or both during a body recomposition phase.

What is a good lean body mass?

There's no universal ideal — LBM varies significantly with height, sex, and build. As a reference, average LBM for men is approximately 60–70 kg and for women approximately 40–50 kg, though athletes may have significantly higher values. What matters more than an absolute number is whether your LBM is stable or growing over time while body fat decreases.

How can I increase my lean body mass?

Resistance training (weightlifting, bodyweight exercises) is the most effective way to increase LBM. Adequate protein intake (1.6–2.2g/kg of body weight or LBM), sufficient calories to support muscle growth, progressive overload in training, and quality sleep all contribute. Building meaningful lean mass takes months to years of consistent effort.

Is lean body mass the same as muscle mass?

No. Lean body mass includes all non-fat tissues: muscles, bones, organs, blood, and water. Muscle mass is a subset of LBM. Muscle typically accounts for approximately 40–50% of total body weight in a healthy adult. DEXA scans can separately quantify muscle, bone, and fat — ordinary scales and formulas can only estimate total LBM.

Lean Body Mass Calculator

Calculate your lean body mass using three clinical formulas. Understand your muscle and fat composition — and set more accurate nutrition and training targets.

Weight (kg)

Height (cm)

Known Body Fat % — optional, for more accuracy

Calculate body fat % first for best results

What is Lean Body Mass?

Lean Body Mass (LBM) is the total weight of your body minus all fat mass. It includes your muscles, bones, organs, connective tissue, blood, and water — essentially everything that isn't fat. It is sometimes called Fat-Free Mass (FFM).

This calculator uses three clinically validated formulas. The **Boer formula** (1984) is the most widely cited and uses height and weight only. The **James formula** (1976) uses a similar approach. The **Hume formula** (1966) is one of the earliest validated equations and is still referenced in pharmacological dosing calculations.

If you know your body fat percentage (from a DEXA scan, navy method, or body fat calculator), entering it gives a more precise result than the formula-based estimate.

Lean body mass is critical for setting accurate protein targets (typically 1.6–2.2g per kg of LBM for muscle building), calculating drug doses in clinical settings, and assessing changes in body composition over time — particularly when the goal is building muscle while losing fat.

Frequently Asked Questions

Lean body mass (LBM) is your total body weight minus all fat. It includes muscle, bone, water, organs, and connective tissue. Unlike fat-free mass, lean body mass sometimes includes a small amount of essential fat (found in the brain, nerves, and cell membranes). It is the metabolically active component of your body weight.

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