What counts as lean body mass?

Everything except fat: muscle, bone, organs, blood, skin and water — typically 70–90% of body weight.

Which formula should I trust?

None is perfect; they generally agree within a few kg. Averaging Boer, James and Hume (or getting a DEXA scan) is the most defensible.

Lean Body Mass Calculator

Computes lean body mass (everything in your body except fat: muscle, bone, organs, blood, skin) from height, weight, gender and age using the Boer, James and Hume formulas side by side, with an implied body-fat percentage.

#lean body mass calculator#lbm#fat free mass#body fat percentage#boer formula

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Gender

MaleFemale

Age 14 or younger?

Uses the Boer child formula (ages 3–14) instead of the adult formulas.

Unit System

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Enter your values in the matching fields — the other unit set is ignored.

Height

Weight

Height (feet)

Height (inches)

Weight

Live mode: results update as you type.

Lean Body Mass (Boer)

53.3 kg (117 lb)

88.8% of 60.0 kg body weight · male formula

Body weight: 60.0 kg
Boer formula: 53.3 kg (117 lb)
James formula: 51.8 kg (114 lb)
Hume formula: 51.2 kg (113 lb)
Average estimate: 52.1 kg (115 lb)
Estimated fat mass: 6.7 kg (15 lb)
Implied body fat: 11.2%

Body composition (Boer estimate)

Lean body mass53.30
Fat mass6.70

Lean body mass by formula

Formula	Lean body mass	Body fat %
Boer	53.3 kg (117 lb)	11.2%
James	51.8 kg (114 lb)	13.7%
Hume	51.2 kg (113 lb)	14.6%

Formula disagreement of a few kg is normal — they were each fit to different reference populations.

Formulas estimate LBM from height and weight alone; DEXA scans are the gold standard for true body composition. Estimates for informational purposes only — not medical advice.

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Formula

Boer (male): LBM = 0.407W + 0.267H − 19.2 · (female): 0.252W + 0.473H − 48.3 · James: 1.1W − 128(W/H)² (male)

• W = weight (kg), H = height (cm).
• Boer is a linear regression; James penalizes high BMI via the (W/H)² term; Hume is a separate linear fit.
• Body fat % = (weight − LBM) ÷ weight × 100.

Pro tips

• LBM is the basis for protein targets and drug dosing — many clinicians dose by LBM, not total weight.
• Strength standards and metabolic rate scale with LBM, so two people of equal weight can burn very different calories.
• Track LBM during a cut: holding it steady means you are losing fat, not muscle.

FAQ

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Lean Body Mass Calculator

#lean body mass calculator#lbm#fat free mass#body fat percentage#boer formula

Formula

Lean body mass

Body fat %

Boer

53.3 kg (117 lb)

11.2%

James

51.8 kg (114 lb)

13.7%

Hume

51.2 kg (113 lb)

14.6%

Formula

Boer (male): LBM = 0.407W + 0.267H − 19.2 · (female): 0.252W + 0.473H − 48.3 · James: 1.1W − 128(W/H)² (male)

• W = weight (kg), H = height (cm).

• Boer is a linear regression; James penalizes high BMI via the (W/H)² term; Hume is a separate linear fit.

• Body fat % = (weight − LBM) ÷ weight × 100.

Pro tips

• LBM is the basis for protein targets and drug dosing — many clinicians dose by LBM, not total weight.

• Strength standards and metabolic rate scale with LBM, so two people of equal weight can burn very different calories.

• Track LBM during a cut: holding it steady means you are losing fat, not muscle.