What is the difference between lean body mass and fat-free mass?

Lean body mass (LBM) and fat-free mass (FFM) are used interchangeably in most contexts. Technically, LBM includes essential fat (found in bone marrow, organs, nervous system) while FFM excludes all fat. The difference is small — typically 2-3% of body weight — and both terms refer to the non-storage-fat component of body composition.

How much protein should I eat per pound of lean body mass?

Research supports 0.7–1.0 g of protein per lb of LBM for general health and muscle maintenance. For active individuals building muscle, 1.0–1.4 g/lb LBM is commonly recommended. For athletes in heavy training or during caloric restriction, up to 1.5 g/lb LBM may be warranted. Using LBM rather than total body weight prevents overestimating protein needs for people with high body fat.

Can I build lean mass while losing body fat simultaneously?

Yes — this is body recomposition. It's most effectively achieved by beginners and by people returning after a training break. It requires adequate protein intake (1+ g/lb LBM), progressive strength training, and a modest caloric deficit (or maintenance calories). Advanced trainees typically need to bulk and cut in phases rather than recompose simultaneously.

How accurate are LBM formula estimates without body fat measurement?

The Boer, James, and Hume formulas estimate LBM from height and weight with a typical error of ±5-8% compared to DEXA scan. They assume average body fat distribution for the sex and height. People at extremes of body composition (very lean or very obese) will see higher formula error. For most individuals, the consensus estimate is a useful working approximation.

❤️Health

How Much of Your Weight Is Lean Muscle vs Fat?

How much of your weight is muscle?

What This Does

Your total body weight is a blunt instrument. It tells you the sum of everything — bone, muscle, water, organ tissue, and body fat — without distinguishing between them. Lean Body Mass (LBM), also called Fat-Free Mass (FFM), is the weight of everything except fat. It includes skeletal muscle, bone, water, connective tissue, and organs. Why does LBM matter? Because it's the metabolically active component of your body. Your basal metabolic rate (the calories you burn at rest) is driven primarily by your lean mass, not your total weight. Two people with the same total weight but different LBM will have meaningfully different caloric needs, different strength potentials, and different body composition. The three most validated LBM estimation formulas — Boer, James, and Hume — use height and body weight to estimate lean mass without requiring a body fat test. These are estimates with inherent variability (body fat percentage from DEXA or hydrostatic weighing is more accurate), but they provide a clinically useful approximation for most people. The consensus of the three formulas reduces individual formula error. LBM has direct applications in nutrition planning (protein targets are often set per kg of LBM), medication dosing, and body recomposition tracking. Knowing your LBM also helps you set more meaningful fitness goals: rather than targeting a scale weight, target a specific LBM + body fat combination.

When Should You Use This?

→Estimating how much of your weight is lean muscle vs body fat
→Setting protein and nutrition targets based on lean mass rather than total weight
→Tracking body recomposition — are you gaining muscle or losing it?
→Understanding your caloric needs relative to your metabolically active lean mass
→Setting body composition goals rather than scale weight targets

Example Scenario

Carlos, 35, is 5'10" and weighs 195 lbs. His body fat % by caliper is 22%, so his fat mass is 42.9 lbs and estimated LBM is 152 lbs. Using LBM formulas: Boer = 155 lbs, James = 156 lbs, Hume = 152 lbs. Consensus: ~154 lbs LBM. His protein target at 0.8g/lb LBM = 123g/day. At 1g/lb LBM (muscle building) = 154g/day. He now has a precise nutrition target tied to his lean mass.

Lean Body Mass Calculator

LBM · Body Fat % · FFMI · Protein Targets · Recomposition

Results update in real time as you adjust any input.

Height

ftin

Body Weight (lbs)

Body Fat % (optional)

Leave blank for formula estimate · DEXA/calipers = more accurate

Goal Body Fat %

Athletic: 8–14% · Fitness: 14–18%

About This Calculator

This lean body mass calculator uses three validated clinical formulas — Boer (1981), James (1976), and Hume (1966) — to estimate LBM from height, weight, and sex, displaying the consensus average as the primary result. An optional measured body fat percentage (from DEXA, calipers, or hydrostatic weighing) overrides the formula estimate for higher accuracy. Results update in real time across both imperial (ft/in/lbs) and metric (cm/kg) unit systems. FFMI, BMI, body fat category, protein targets, and recomposition targets all update live.

The Composition tab renders a donut PieChart (LBM in accent vs fat mass in red) beside a colour-coded BF% spectrum bar showing where your current body fat falls among Essential, Athletic, Fitness, Average, and Obese ranges. A RadarChart plots five fitness dimensions: Leanness, FFMI, Lean Mass %, BMI Status, and Composition Score. The Formulas tab shows a bar chart of LBM from all three formulas plus the consensus, with a reference line at the consensus value. The Recomp tab shows a grouped bar chart of target weight and fat-to-lose at four BF% goal levels.

Dynamic accent colours reflect body fat category: emerald (Athletic), green (Fitness), amber (Average), red (Obese Risk), indigo (Essential). The FFMI scale runs from Below Average through Excellent to Exceeds Natural Max, with each range colour-coded. Protein targets are calculated from LBM rather than total weight, which avoids overestimation at higher body fat percentages. Recomposition targets assume LBM preservation and calculate the theoretical target weight at each BF% goal using the inverse formula: Target Weight = LBM / (1 − Goal BF%).

Results are estimates only and do not constitute medical advice. Consult a qualified healthcare professional before making health decisions.