Free Lean Body Mass Calculator: Boer, James & Hume Formulas Compared
Estimate lean body mass (everything except fat) with three published formulas at once, or directly from your body fat percentage.
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About this calculator
Lean body mass (LBM) is your total weight minus body fat. It includes muscle, bone, organs, skin and water. It matters for setting protein targets, calculating metabolic rate and, in medicine, for dosing certain drugs and anaesthetics.
No single formula is perfect, so this calculator shows three well-known ones side by side and averages them. If you know your body fat percentage, the direct calculation is more reliable.
How it works
Boer: men 0.407 × W + 0.267 × H − 19.2 · women 0.252 × W + 0.473 × H − 48.3
James: men 1.1 × W − 128 × (W/H)² · women 1.07 × W − 148 × (W/H)²
Hume: men 0.3281 × W + 0.33929 × H − 29.5336 · women 0.29569 × W + 0.41813 × H − 43.2933
From body fat: LBM = weight × (1 − body fat %)
W = weight in kg, H = height in cm.
How to read your result
The formulas can differ by several kilograms. Look at the range rather than a single number. The James formula tends to lower LBM at higher weights, while Boer is the most widely used in clinical research. A higher LBM relative to weight generally means a better body composition.
Worked example
A man, 80 kg, 180 cm, with measured body fat of 20%.
| From your body fat % | 64 kg Most accurate when body fat is measured (DEXA/BIA) |
| Average of three formulas | 60.6 kg 76% of body weight |
| Boer formula | 61.4 kg |
| James formula | 62.7 kg |
| Hume formula | 57.8 kg |
Frequently asked questions
What is lean body mass?
Lean body mass is everything in your body that is not fat: muscle, bone, organs, skin and body water.
Is lean body mass the same as muscle mass?
No. LBM includes bones, organs and water as well as muscle. Skeletal muscle mass is a smaller subset.
Which formula is best?
Boer is the most commonly used clinically, but all three are estimates. Measured body fat gives a better answer.
How do I increase lean body mass?
Resistance training, adequate protein and enough calories. Gains are slow, typically 0.25–0.5 kg per month for trained individuals.
Limitations and when not to use
Equations are population estimates and are not validated for children or for pregnancy.
Sources and references
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol 1984;247:F632–F636.
- Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 1966;19:389–391.
- James WPT. Research on obesity. HMSO, London, 1976.
Last updated: 2026-10-09