Free Body Composition Tool

Lean Body Mass Calculator

What is lean body mass? Lean body mass (LBM) — also called fat-free mass — is the total weight of everything in your body except fat: muscles, bones, organs, connective tissue, and water. It typically represents 60–90% of total body weight depending on fitness level. Accurately knowing your LBM allows you to set science-based protein targets (usually 1.6–2.2 g per kg of LBM), calculate a more precise TDEE, and track actual muscle gain over time.

LBM Composition Engine

STATUS: READY_FOR_INPUT

Biological Sex

Weight

Height

Body Fat % (optional — leave blank to use formula method)

Understanding Lean Body Mass

What is Lean Body Mass?

LBM encompasses all metabolically active tissue: skeletal muscle, cardiac muscle, the liver, kidneys, brain, skin, bone mineral, and body water. Unlike muscle mass (which refers only to skeletal muscle), LBM includes every component except adipose (fat) tissue. This distinction matters because fat is largely metabolically inactive — meaning LBM drives almost all of your resting calorie expenditure. A higher LBM translates directly to a higher BMR and daily calorie burn.

Why LBM Matters for Nutrition

Protein targets based on total body weight overestimate needs for people with high body fat. Basing protein intake on LBM (1.6–2.2 g/kg) gives a more accurate and personalised target. Similarly, TDEE calculators using LBM (like the Katch-McArdle equation) are more accurate for people outside the "average" body fat range. Tracking your LBM over weeks and months is the clearest indicator of whether you are building or retaining muscle during a cut.

Track Body Composition Over Time

Body composition changes slowly. The FitScanned app tracks your nutrition daily with AI scanning — so your protein and calorie targets always reflect your current lean mass goals.

Download iOS Android App

Quick Facts

✓LBM = Total weight minus fat mass
✓Typical LBM is 60–90% of total weight
✓Protein target: 1.6–2.2 g per kg LBM
✓Natural male FFMI cap: ~25 kg/m²
✓Uses Boer, James & Hume formulas averaged

Common Questions

What is the difference between lean body mass and muscle mass?↓

Lean body mass includes all non-fat tissue: muscles, bones, organs, and body water. Muscle mass refers specifically to skeletal muscle only. LBM is always higher than muscle mass because it includes bone, water, and organ weight.

Is lean body mass the same as fat-free mass?↓

In practice, these terms are used interchangeably. Some researchers define a small distinction — "fat-free mass" strictly excludes all lipid content, while "lean body mass" may include a small amount of essential fat in cell membranes and the nervous system. For practical nutrition purposes, they are equivalent.

How do I increase my lean body mass?↓

The primary driver of LBM growth is progressive resistance training combined with adequate protein intake (1.6–2.2 g/kg LBM) and sufficient total calories. A moderate caloric surplus of 200–400 kcal/day optimises muscle gain with minimal fat gain.

Why does lean body mass matter for calculating protein needs?↓

Protein requirements scale with metabolically active tissue, not total body weight. A person with 100 kg total weight and 30% body fat has 70 kg of LBM and needs roughly 112–154 g of protein daily — not 160–220 g based on total weight. LBM-based targets are more accurate, especially for people with higher body fat.

What is a good FFMI for natural athletes?↓

Research by Kouri et al. suggests natural (drug-free) male athletes typically fall between 18–22 FFMI, with values above 25 considered near the physiological ceiling. For females, 15–18 FFMI is the natural athletic range. These are averages — elite genetics can produce higher values naturally.