Lean Body Mass Calculator

We help digital brands grow faster. But with a name like ours, building the internet’s most accurate Lean Body Mass calculator was inevitable. We fixed the broken formulas that mislabel athletes and muscular builds as obese. Enjoy!

What Makes This the Best Lean Body Mass Calculator

Most tools show a single estimate and call it a day. Ours runs multiple validated equations side-by-side, highlights the method best suited to your inputs, and shows the spread so you understand uncertainty. It also supports pediatric calculations, high-BMI routing, and (optionally) body-fat–based lean mass when you already know your BF%.

Multi-equation output: Boer, James, Hume, Janmahasatian (high-BMI), Peters (children).
Confidence range: min–max across methods so you see variance.
Optional BF% override: when BF% is known, we compute LBM = Weight × (1 – BF%).
FFMI & Lean %: context beyond a single kilogram figure.
Fast + accessible: keyboard friendly, proper headings, and clear labels.

How the Calculator Works

Enter sex, age, height, and weight (plus BF% if you have it).
We compute Lean Body Mass (LBM) with several peer-reviewed equations.
Children ≤14 → Peters pediatric formula. Higher BMI → Janmahasatian.
You get: LBM (kg/lb), Lean %, FFMI, and a confidence range across methods.

Lean Body Mass Formulas (Adults)

In all formulas below, W = weight (kg), H = height (cm).

Boer (1984)

Men:    LBM = 0.407·W + 0.267·H − 19.2
Women:  LBM = 0.252·W + 0.473·H − 48.3

James (1976)

Men:    LBM = 1.10·W − 128·(W/H)²
Women:  LBM = 1.07·W − 148·(W/H)²

Hume (1966)

Men:    LBM = 0.32810·W + 0.33929·H − 29.5336
Women:  LBM = 0.29569·W + 0.41813·H − 43.2933

Janmahasatian (High BMI)

BMI = W / ( (H/100)² )

Men:    LBM = ( 9270·W ) / ( 6680 + 216·BMI )
Women:  LBM = ( 9270·W ) / ( 8780 + 244·BMI )

Lean Body Mass Formula (Children)

Peters (2011)

eECV = 0.0215 · W^0.6469 · H^0.7236
LBM  = 3.8 · eECV

LBM vs. Fat-Free Mass

LBM: everything except storage fat; includes organs, water, bone, and essential fat.
FFM: subtracts all fat (including essential fat). Usually 2–3% lower than LBM in men, 5–12% lower in women.
DEXA “Lean”: often defined differently; not identical to pure muscle mass.

Which Equation Should You Trust?

General adults: Boer/Hume.
Higher BMI: Janmahasatian.
Children: Peters.
If BF% known: LBM = W × (1 − BF%) is a good check.

FFMI (Fat-Free Mass Index)

FFMI scales fat-free mass to height (like BMI but for lean tissue). Typical trained male FFMI is in the low-20s; women lower. Use FFMI to compare across heights, not as a diagnostic.

FAQs

What is lean body mass?

LBM = body weight minus storage fat. Includes bone, water, organs, and essential fat. Not the same as pure muscle.

Why do formulas differ?

They were derived from different populations. At high/low BMIs some drift; showing multiple gives context.

Is LBM the same as FFM?

No. FFM excludes essential fat; it’s typically a bit lower than LBM.

What if I’m very muscular?

Equations may under-estimate outliers. If you know BF%, compare BF%-based LBM with the range.

Can I use this for dosing?

Some formulas are used clinically, but dosing must be handled by medical professionals.

References

Boer P. Am J Physiol. 1984;247:F632–F635.
James W. Research on Obesity. 1976.
Hume R. J Clin Pathol. 1966;19(4):389–91.
Peters AM et al. Br J Anaesth. 2011;106(5):719–23.
Janmahasatian S et al. Clin Pharmacokinet. 2005;44(10):1051–65.