Wood Movement Shrinkage Calculator
Wood expands and contracts across the grain as it gains and loses moisture, and ignoring this is the most common cause of cracked panels and stuck drawers. This calculator estimates dimensional change for a board from a moisture content shift, using its width, the species shrinkage coefficient (tangential or radial), and the fiber saturation point. Below fiber saturation, movement is close to linear with moisture content, so the math is straightforward. Shrinkage values are species-specific, so they are user-editable inputs taken from the USDA Forest Products Laboratory Wood Handbook.
Wood movement formula
MC change = final MC - initial MC
Fractional change = (coefficient / 100) * MC change / FSP
Dimensional change = width * fractional change
Final width = width + dimensional change
A negative dimensional change means the board shrinks as it dries; a positive value means it swells as it gains moisture. The coefficient is the total green-to-oven-dry shrinkage for the chosen grain direction and species.
Practical notes
- Use tangential coefficients for flatsawn faces and radial for quartersawn.
- Tangential movement is usually about 1.5 to 2 times radial movement.
- Get species shrinkage values from the USDA Wood Handbook.
- Acclimate wood to its service humidity before final fitting.
- Movement along the grain (length) is tiny and ignored here.
Wood movement: frequently asked questions
How is wood dimensional change calculated?
Change in width = current width x shrinkage coefficient x (final moisture content - initial moisture content) / fiber saturation point. Below the fiber saturation point (about 28 to 30 percent), wood shrinks and swells roughly linearly with moisture content. The shrinkage coefficient differs for the tangential and radial directions and by species.
What is the fiber saturation point?
The fiber saturation point is the moisture content, around 28 to 30 percent for most species, below which the cell walls begin losing bound water and the wood changes size. Above it, free water in the cell cavities leaves without dimensional change. This calculator uses a default of 28 percent, which you can edit.
Where do I get the shrinkage coefficient for my species?
The USDA Forest Products Laboratory Wood Handbook publishes total tangential and radial shrinkage values (green to oven-dry) for hundreds of species. Tangential movement (along growth rings) is typically nearly double radial movement (across rings). Enter the percentage that matches your species and the relevant grain direction.
Why does tangential movement exceed radial movement?
Wood is anisotropic. Tangential shrinkage (the direction following the growth rings, roughly the board face for flatsawn lumber) is usually about 1.5 to 2 times the radial shrinkage (across the rings). This is why flatsawn boards cup and quartersawn boards stay flatter.
How do I avoid problems from wood movement?
Acclimate wood to its in-service environment before building, design joinery that lets panels float (frame and panel, breadboard ends with elongated holes), and orient grain consistently. Calculating expected seasonal movement lets you size gaps and slots so the piece does not crack or bind.
Official sources
- USDA Forest Products Laboratory: Wood Handbook, shrinkage and moisture relations.
- USDA Forest Service: Forest Service research publications.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.