Lean body mass calculator
Lean body mass, or LBM, is body weight minus fat mass.
The Hume 1966 equations estimate LBM from height, weight and sex. An optional body fat percentage gives a separate estimate by subtracting fat mass from weight.
Men
LBM kg = 0.32810 × W + 0.33929 × H − 29.5336
Women
LBM kg = 0.29569 × W + 0.41813 × H − 43.2933
W means body weight in kilograms. H means standing height in centimeters, measured without shoes. Hume 1966, checked October 2, 2026.
| Method | kg | lb | Percent of weight |
|---|---|---|---|
| Hume 1966 formula estimate | 56.1 | 123.7 | 70.1 |
| From your body fat percentage Estimate |
Boer 1984 and James 1976 are omitted because their equations could not be checked against the original papers.
Work through 175 cm and 80 kg
For a man at 175 cm and 80 kg, the Hume calculation is
- 0.32810 × 80 = 26.248
- 0.33929 × 175 = 59.37575
- 26.248 + 59.37575 − 29.5336 = 56.09 kg, rounded to two decimals.
The displayed estimate is 56.1 kg or 123.7 lb, 70.1 percent of body weight.
Using a measured body fat figure of 20 percent at the same 80 kg gives 80 × (1 − 0.20) = 64.0 kg, or 141.1 lb. That is 80.0 percent of body weight.
These calculations answer different questions. Hume predicts from height and weight what lean mass a person of that size had on average in the 1966 study group. The body fat method uses a measured body fat figure, so its result changes with body fat even when height and weight stay the same.
Hume estimates at other heights and weights
Each row uses the printed Hume equation. Feet and inches are rounded to the nearest inch for display, and the calculation uses centimeters.
| Sex | Height cm and ft in | Weight kg and lb | Hume estimate kg | Hume estimate lb | Percent of weight |
|---|---|---|---|---|---|
| Woman | 160 cm (5 ft 3 in) | 60 kg (132.3 lb) | 41.3 | 91.2 | 68.9 |
| Woman | 165 cm (5 ft 5 in) | 70 kg (154.3 lb) | 46.4 | 102.3 | 66.3 |
| Woman | 170 cm (5 ft 7 in) | 85 kg (187.4 lb) | 52.9 | 116.7 | 62.3 |
| Man | 170 cm (5 ft 7 in) | 65 kg (143.3 lb) | 49.5 | 109.1 | 76.1 |
| Man | 175 cm (5 ft 9 in) | 80 kg (176.4 lb) | 56.1 | 123.7 | 70.1 |
| Man | 185 cm (6 ft 1 in) | 100 kg (220.5 lb) | 66.0 | 145.6 | 66.0 |
Where the Hume equations came from
Hume fitted the equations on 56 adults in Glasgow, 29 men and 27 women. The men were 40 to 77 years old, with a mean age of 61. The women were 37 to 80, with a mean age of 60.
The study worked out lean body mass from total body water measured by antipyrine dilution. The multiple correlation coefficient r was 0.957 for men and 0.8298 for women.
The standard deviation of the differences between measured and predicted values was 2.307 kg for men and 5.372 kg for women. Hume described the men's error as acceptable for an individual prediction. The paper said the women's error of 5.4 kg might be a little large for one person but was satisfactory for comparing groups.
Why Boer and James are left out
This calculator includes only the height and weight equations checked against the original paper. Boer's 1984 paper is paywalled, and the PubMed abstract does not contain the equations, so this page leaves them out.
James's 1976 report, Research on obesity, is a printed report with no online copy. Its equation could not be checked, so it is also left out.
Height and weight compared with body fat
For any fixed height, weight and sex, Hume returns the same prediction from its study group. It has no input for body fat.
The other line calculates weight kg × (1 − body fat percentage ÷ 100). It reflects the body fat figure entered, including a change in that figure at an unchanged weight.
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Questions about lean body mass
What is an LBM calculator?
An LBM calculator estimates lean body mass. This page uses height, weight and sex in the Hume 1966 equations.
Which formulas are included?
Hume 1966 provides the height and weight estimate. Entering body fat adds an estimate equal to body weight minus fat mass.
Why can the body fat result differ?
Body fat contributes directly to the body fat calculation. The Hume prediction uses height, weight and sex, so changing body fat alone does not change it.
How does this page calculate fat-free mass?
The body fat line subtracts fat mass from body weight. Hume estimated lean body mass from total body water in the original study.
Sources and conversions
Hume R. Prediction of lean body mass from height and weight. Journal of Clinical Pathology, 1966, volume 19, pages 389 to 391. PubMed and full paper DOI, checked October 2, 2026.
Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. American Journal of Physiology, 1984, volume 247, pages F632 to F636. PubMed, checked October 2, 2026. The original equations were unavailable for verification.
James WPT. Research on obesity, a report of the DHSS/MRC group. HMSO, London, 1976. Checked October 2, 2026. No online copy was available to check the equation.
TrueCal product facts, checked October 2, 2026.
The conversions used here are 1 inch = 2.54 centimeters and 1 pound = 0.45359237 kilograms. Results in pounds use 1 kg = 2.20462 lb.
For a calculation using fat-free mass and height, open the FFMI calculator.
The TDEE calculator is a separate tool for estimating daily calorie expenditure.
Other topics are collected in the TrueCal guides.