Samenvatting
Lean body mass (LBM) is your total body weight minus all fat mass — it includes muscles, bones, organs, water, and connective tissue. Unlike BMI, which treats all weight the same, LBM distinguishes between fat and everything else, making it useful for drug dosing, protein targets, and tracking body composition during fat loss.
Three estimation formulas are widely used: Boer (1984), James (1976), and Hume (1966). Each uses only height and weight but applies different regression coefficients derived from separate study populations. If you know your body fat percentage (from DEXA, calipers, or another method), the direct method — LBM = weight × (1 − BF%/100) — is more accurate than any estimation formula.
Hoe het werkt
All three formulas use linear regression equations derived from body water measurements (via isotope dilution or antipyrine space). They estimate the portion of body weight that is not fat, based on height and weight alone.
The formulas produce different estimates because they were derived from different study populations:
- Boer studied 54 healthy adults and focused on normalising body fluid volumes
- Hume studied 56 adults using antipyrine-space total body water measurements
- James compiled obesity research for a UK government (DHSS/MRC) report
None of these formulas account for age, ethnicity, or fitness level — they estimate a population average for a given height and weight.
The formulas
Boer (1984)
Where
Where
James (1976)
Where
Where
Hume (1966)
Where
Where
Direct method (from body fat %)
Where
When body fat percentage is known, this direct calculation is used as the primary result. The three estimation formulas are still shown for comparison.
Worked examples
Male, 80 kg, 180 cm (no body fat % known)
Average male: 80 kg, 180 cm
Boer formula
= 61.42 kg
James formula
= 62.72 kg
Hume formula
= 57.79 kg
Average of three formulas
= 60.64 kg
Result
Lean body mass ≈ 60.6 kg (75.8% of body weight)
Female, 65 kg, 165 cm
Average female: 65 kg, 165 cm
Boer formula
= 46.13 kg
James formula
= 46.58 kg
Hume formula
= 44.92 kg
Average of three formulas
= 45.88 kg
Result
Lean body mass ≈ 45.9 kg (70.6% of body weight)
Invoer uitgelegd
- Sex — required because male and female formulas use different regression coefficients. Males typically have higher lean mass at the same height and weight.
- Height — in centimetres (or feet/inches in imperial mode). Taller individuals generally have more lean mass.
- Weight — in kilograms (or pounds in imperial mode). Heavier individuals have more lean mass, though the proportion depends on body fat.
- Body fat % (optional) — if known from DEXA, calipers, or bioimpedance, the direct method replaces the formula average.
Uitvoer uitgelegd
- Lean body mass — the primary result, in kg or lbs. When body fat % is provided, this uses the direct method. Otherwise, it averages the three formulas.
- Fat mass — total weight minus lean body mass.
- LBM % — lean mass as a percentage of total weight.
- Formula comparison — shows all three formula results side by side, so you can see the range of estimates.
Aannames en beperkingen
- Estimation only — these formulas use population-level regression. Individual variation (muscle mass, bone density, hydration) can cause errors of ±5–13 kg compared to imaging methods like CT or DEXA (Aitken et al., 2016).
- Not validated for extreme body compositions — the original studies used healthy adults of moderate build. The formulas may be less accurate for very lean athletes or individuals with severe obesity.
- Boer is preferred for obese individuals — it was specifically designed to normalise fluid volumes and produces closer estimates in this population.
- Age not accounted for — lean mass naturally declines with age, but none of these formulas include an age term.
- No formula beats a direct measurement — if you have access to a DEXA scan or reliable body fat measurement, the direct method (LBM = weight × (1 − BF%/100)) will always be more accurate.
Verificatie
| Test case | Formula | Expected | Our result | Source |
|---|---|---|---|---|
| Male, 80 kg, 180 cm | Boer | 61.42 kg | 61.42 kg | Hand calculation from published coefficients |
| Male, 80 kg, 180 cm | James | 62.72 kg | 62.72 kg | Hand calculation from published coefficients |
| Male, 80 kg, 180 cm | Hume | 57.79 kg | 57.79 kg | Hand calculation from published coefficients |
| Female, 65 kg, 165 cm | Boer | 46.13 kg | 46.13 kg | Hand calculation from published coefficients |
| Female, 65 kg, 165 cm | James | 46.58 kg | 46.58 kg | Hand calculation from published coefficients |
| Female, 65 kg, 165 cm | Hume | 44.92 kg | 44.92 kg | Hand calculation from published coefficients |
| Male, 80 kg, 180 cm, BF=16% | Direct | 67.20 kg | 67.20 kg | Weight × (1 − 0.16) |
| Male, 100 kg, 190 cm | Boer | 72.23 kg | 72.23 kg | calculator.net cross-check |
Sources
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