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Lean Body Mass Calculator
Estimate how much of your body weight is lean tissue using three published equations, the Boer, James and Hume formulas, and see the implied fat mass and body fat percentage from each.
What lean body mass includes
Lean body mass (LBM) is everything in the body except stored fat: muscle, bone, organs, skin, connective tissue and the water they hold. It is not the same as muscle mass, and it is sometimes confused with fat-free mass, which excludes essential fat as well. LBM is used to size doses of some anaesthetic drugs, to set protein and calorie targets, and to track whether weight lost during a diet came from fat or from lean tissue.
True LBM needs a body-composition scan such as DEXA or a carefully performed hydrostatic weighing. The formulas here estimate it from height and weight alone, so they cannot tell a muscular person from a heavier person with the same measurements.
The three equations
With weight W in kilograms and height H in centimetres:
| Formula | Men | Women |
|---|---|---|
| Boer (1984) | 0.407 W + 0.267 H − 19.2 | 0.252 W + 0.473 H − 48.3 |
| James (1976) | 1.1 W − 128 (W ÷ H)2 | 1.07 W − 148 (W ÷ H)2 |
| Hume (1966) | 0.3281 W + 0.33929 H − 29.5336 | 0.29569 W + 0.41813 H − 43.2933 |
For a man of 80 kg and 180 cm they give 61.4, 62.7 and 57.8 kg. The spread of nearly five kilograms is typical and tells you how uncertain the estimate is.
Using the result sensibly
- Look at the range: if the three formulas disagree widely, regard all of them as approximate.
- Compare to body fat: the fat share shown here is only implied. Cross-check with the body fat calculator, which uses a different input set.
- Track change over time: because the inputs are only weight and height, a drop in weight lowers LBM in the formulas even if you lost pure fat. For real changes use skinfolds, a scan or measured strength.
Limits and cautions
The equations were derived from adult samples and are not meant for children, teenagers or pregnancy. Athletes with a lot of muscle, older people with low muscle mass, and people with oedema, kidney or heart disease can differ greatly from the estimate. Do not use this page to dose medicines or to diagnose sarcopenia or obesity. It is educational and not medical advice.
Worked example
A woman 165 cm tall weighing 65 kg wants to compare the three formulas.
Inputs
| Sex | Female |
|---|---|
| Units | Metric (cm, kg) |
| Height | 165 |
| Weight | 65 |
Result
Average of three formulas; about 29.4% of your weight is estimated as non-lean mass.
| Boer | 46.1 kg |
|---|---|
| James | 46.6 kg |
| Hume | 44.9 kg |
| Average | 45.9 kg |
Lean mass, fat mass and implied fat percentage
| Formula | Lean mass | Fat mass | Fat share |
|---|---|---|---|
| Boer | 46.1 kg | 18.9 kg | 29.0% |
| James | 46.6 kg | 18.4 kg | 28.3% |
| Hume | 44.9 kg | 20.1 kg | 30.9% |
| Average | 45.9 kg | 19.1 kg | 29.4% |
Medical disclaimer: This tool is for education and general planning. It is not medical advice and does not diagnose any condition. If you are pregnant, under 18, have an eating-disorder history or a medical condition, speak to a doctor or registered dietitian before changing your diet or exercise.
Frequently asked questions
What is lean body mass?
It is your total body weight minus stored fat. It includes muscle, bone, organs, skin and body water, so it is larger than muscle mass alone.
Which lean body mass formula is the most accurate?
None is clearly best for all bodies. Boer is often preferred for drug dosing research and James is widely used, while Hume was an earlier fit. Reading all three shows the uncertainty.
How is lean mass different from fat-free mass?
Lean mass in clinical use usually includes a small amount of essential fat in organs and nerves, while fat-free mass excludes all fat. The difference is small, about two to five percent of body weight.
Can these formulas measure muscle gain?
Not reliably. They use only height and weight, so building muscle while losing fat can leave the estimate unchanged or even lower. A body-composition scan or tape and strength tracking works better.
Are the results valid for children?
No. The equations were built on adults and do not capture growth. Children should be assessed by a paediatric professional using growth charts.
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References and sources
- Boer P. (1984). Estimated lean body mass as an index for normalization of body fluid volumes in humans. American Journal of Physiology 247(4):F632-F636.
- James WPT (1976). Research on obesity. London: Her Majesty Stationery Office.
- Hume R. (1966). Prediction of lean body mass from height and weight. Journal of Clinical Pathology 19(4):389-391.