How to use the wood shrinkage calculator
- Measure width across the grain.
- Enter the expected moisture content of the wood at each condition, not relative air humidity.
- Use a movement coefficient appropriate to the species and radial or tangential direction. The default is illustrative.
The formula
Worked example
A 300 mm panel drying from 12% to 6% moisture with a 0.25% movement coefficient shrinks by approximately 4.5 mm to 295.5 mm.
Before you measure and cut
Flatsawn and quartersawn boards move differently. Longitudinal movement is usually much smaller and is not modeled here.
The inputs are limited to 0–30% moisture content for this simplified below-fiber-saturation model. Fiber saturation varies with material; the tool is an estimate, not a drying schedule.
Frequently asked questions
Can I enter relative humidity?
No. Relative humidity of the air and moisture content of wood are different quantities. Enter wood moisture content, preferably measured or based on a suitable equilibrium-moisture reference.
Why is the result only approximate?
Movement is not perfectly linear, and species, sawing orientation, restrained joints, temperature, and moisture gradients all matter.
Reference
USDA Forest Products Laboratory: Wood Handbook. Material properties and setup conventions depend on the specific product.