How is lean body mass calculated?

If you know body fat %, LBM = weight × (1 − body fat % / 100). If not, formulas estimate LBM from height, weight, and sex. This calculator uses Boer as the primary estimate and also shows James and Hume for comparison.

Which LBM formula is most accurate?

Boer is widely considered the most accurate height/weight estimate for adults across a broad range of body types. James and Hume are common alternatives. For obese individuals, some clinicians prefer equations like Janmahasatian. Direct calculation from a measured body fat % (DEXA, Bod Pod, reliable tape) is better than any height/weight estimate.

What is FFMI and why does it matter?

Fat-Free Mass Index (FFMI) = LBM (kg) ÷ height (m)². It normalizes lean mass for height. Roughly: men 18–20 average, 20–22 above average, 22–25 highly muscular; women 14–16 average, 16–18 above average, 18+ highly muscular. Values above ~25 in men are rare without enhancement.

How can I increase my lean body mass?

Progressive resistance training, protein at about 1.6–2.2 g per kg body weight (or per kg LBM for tighter targets), enough total calories (small surplus or at least maintenance), and 7–9 hours of sleep. Track LBM over weeks, not day to day.

Is lean body mass the same as muscle mass?

No. Muscle is only part of lean body mass. LBM also includes bone, organs, blood, water, and connective tissue. When LBM rises from training, most of the change people care about is muscle plus associated water and glycogen — but the number is not pure muscle kilograms.

Lean Body Mass Calculator

Estimate your lean body mass (LBM), fat mass, and FFMI. Compare Boer, James, and Hume formulas — or enter a known body fat % for a direct calculation.

Lean body mass is your weight minus stored fat. Use height + weight for an estimate (Boer is primary), or enter body fat % for the most accurate LBM from the scale.

Boer (1984), James, and Hume height/weight equations. Direct mode uses LBM = weight × (1 − BF%/100). Educational estimate — not a DEXA scan.

Sex

Male Female

Height (cm) Weight (kg) Body fat % From DEXA, Bod Pod, Navy tape, or a reliable estimate — not required for formula mode

How to Use This Lean Body Mass Calculator

Choose Estimate if you only know height and weight — we’ll run Boer (primary), James, and Hume. Choose I know my body fat % for a direct LBM calculation: weight × (1 − BF%/100). Results include fat mass, body fat %, and FFMI.

What Is Lean Body Mass?

Lean body mass (LBM), sometimes called fat-free mass, is everything except stored body fat — muscle, bone, organs, blood, water, glycogen, and connective tissue. It is not the same as “muscle mass,” but when LBM rises from training, the change you care about is mostly muscle plus associated water and glycogen.

LBM matters because it drives much of your resting calorie burn, helps set smarter protein targets, and shows whether a diet is stripping fat or muscle. Two people at 80 kg can have very different LBM — and very different nutrition needs.

How to Calculate Lean Body Mass

1) Direct method (best if you know BF%)

LBM = weight × (1 − body fat % ÷ 100)

Example: 80 kg at 20% body fat → LBM = 80 × 0.80 = 64 kg; fat mass = 16 kg.

2) Height/weight formulas (when BF% is unknown)

This lean body mass calculator compares the three formulas most people search for:

Formula	Men	Women
Boer (primary)	0.407×W + 0.267×H − 19.2	0.252×W + 0.473×H − 48.3
James	1.1×W − 128×(W/H)²	1.07×W − 148×(W/H)²
Hume	0.32810×W + 0.33929×H − 29.5336	0.29569×W + 0.41813×H − 43.2933

W = weight in kg, H = height in cm. Boer is generally preferred for adults; we still show James and Hume so you can see the spread (like calculator.net).

What Is FFMI?

Fat-Free Mass Index = LBM (kg) ÷ height (m)². It normalizes lean mass for height the way BMI normalizes total weight:

FFMI	Men	Women
Below average	< 18	< 14
Average	18–20	14–16
Above average	20–22	16–18
Highly muscular	22–25	18–21
Rare / exceptional	25+	21+

Using LBM for Cutting and Bulking

Cutting: Keep protein high relative to LBM (often ~2.0–2.5 g/kg LBM) and aim to hold LBM steady while fat mass drops.
Bulking: A small surplus plus progressive lifting should raise LBM over months — not just scale weight.
Recomp: Beginners and returning lifters can gain LBM while losing fat at maintenance calories.

Pair this tool with our body fat calculator, protein intake calculator, and body recomposition calculator.

How Accurate Are These Estimates?

Height/weight formulas are population estimates (± a few kg for most adults). They can misread very muscular or very obese people. Rough accuracy ranking for body-fat inputs:

Method	Typical accuracy	Notes
DEXA	±1–2%	Best common lab option
Bod Pod / hydrostatic	±1–3%	Good when protocol is strict
Navy / tape	±2–4%	Free; use consistent landmarks
BIA / smart scale	±3–5%+	Hydration swings results
Boer / James / Hume	Estimate only	No BF% needed; compare all three

How to Increase Lean Body Mass

Progressive resistance training — add load or reps over time on compounds.
Protein 1.6–2.2 g/kg body weight (or higher relative to LBM when cutting).
Enough calories — small surplus for growth; avoid chronic severe deficits.
Sleep 7–9 hours — recovery is when tissue remodeling happens.
Re-check monthly — same method each time (same formula or same BF% source).

Disclaimer: Formula-based LBM is an educational estimate, not a clinical measurement. Medication dosing and medical decisions should use clinician-approved methods, not a website calculator alone.

How this calculator works

In estimate mode we compute Boer, James, and Hume LBM from height, weight, and sex, then derive fat mass, BF%, and FFMI from Boer. In direct mode we use your entered body fat % for LBM and still show formula estimates for comparison when height is provided.

Frequently asked questions

What is lean body mass?+

Everything except stored fat — muscle, bone, organs, water, and connective tissue. More useful than scale weight for calories, protein, and progress tracking.

Which formula should I trust — Boer, James, or Hume?+

Use Boer as the default adult estimate. Check James and Hume to see the range. If the three disagree a lot, get a better BF% measurement and use direct mode.

Is LBM the same as muscle?+

No. Muscle is only part of lean mass. Bones, organs, and water are included too — so don’t treat every LBM kilo as pure muscle.

What is a good FFMI?+

For men, ~18–20 is average and 20–22 is above average with training. For women, ~14–16 is average and 16–18 is above average. Context and genetics matter more than chasing a single number.

How do I increase lean body mass?+

Lift progressively, eat enough protein and calories, sleep well, and track LBM monthly with the same method. Pair with a high-protein meal plan if you need structure.