Timber is a hygroscopic material; it absorbs or releases moisture from the surrounding air until its moisture content (MC) reaches equilibrium with the ambient relative humidity. The moisture content is expressed as a percentage of the wood’s oven‑dry weight and typically ranges from 5 % in dry indoor conditions to 30 % or more in outdoor or storage environments.
When the MC changes, the wood dimensions change proportionally. This dimensional change, called shrinkage (or swelling when MC increases), is governed by a material‑specific shrinkage coefficient (k) that varies with grain direction. The linear shrinkage for a given change in moisture content is calculated by multiplying the original length by the coefficient and the moisture‑content difference.
L_{0} = original length (mm)
k = shrinkage coefficient (mm per % MC per mm)
MC_{i} = initial moisture content (%)
MC_{f} = final moisture content (%)
Accurate prediction of shrinkage is essential for structural design, allowing engineers to anticipate dimensional tolerances, joint gaps, and potential stresses in timber members as they season or are exposed to varying climatic conditions.
How does moisture content affect timber dimensions?
What is the typical range of moisture content in timber?
How does temperature affect moisture content in timber?
What is the relationship between moisture content and shrinkage in timber?
How can I calculate the moisture content of timber?
What factors should I consider when using this calculator?
How does shrinkage affect the use of timber in construction?
Results are for informational purposes only and do not constitute professional advice.