Measurement basis
Solid wood changes dimension as moisture content changes, especially across the grain. This calculator estimates that change using the board width, two moisture-content readings, and a coefficient appropriate to the wood and grain orientation. The coefficient is entered per one percentage-point change in moisture content, so its units matter. The default is only an example and must not be treated as a species recommendation. Use the result to explore a potential seasonal range when planning panel clearances or fastening slots. The simple linear model has a limited working range and does not describe every moisture condition.
Geometry, units and worked example
A worked example
A 24 in board changing from 8% to 12% moisture content at a supplied coefficient of 0.0025 changes by 0.24 in, for an estimated final width of 24.24 in.
Enter consistent dimensions
- Measure the panel dimension across the grain.
- Estimate a realistic initial and final moisture content for the service environment.
- Supply a compatible radial or tangential coefficient and interpret the signed change.
Where the model stops
- A shrinkage percentage from green to oven-dry is not directly the per-point coefficient requested here. Do not substitute it unchanged.
- Flat-sawn and quarter-sawn material move differently. Select data that matches the grain orientation.
- Plywood, composite panels, and restrained assemblies do not follow this simple solid-wood model.
Frequently asked questions
What does a negative wood movement result mean?
It means the model predicts shrinkage because the final moisture content is lower than the initial value.
Can I use the default coefficient for every species?
No. It is an illustrative input. Obtain an appropriate coefficient with the same unit convention for your material.
Does the calculator cover moisture above fiber saturation?
No. The linear relationship is intended as a planning estimate below that region and becomes unsuitable outside its source data range.
Calculation method: JICWH methodology. Examples are planning assumptions, not product recommendations.