Wood Movement Predictor

What this estimate does and does not do

This calculator estimates across-grain wood movement from moisture-content change. It is meant for woodworking layout and joinery planning: tabletops, cabinet doors, frame-and-panel work, drawer fronts, wide shelves, breadboard ends, and solid-wood panels.

It does not replace moisture-meter readings, species-specific technical data, or good joinery design. It also does not model warping, cupping, twist, case construction, veneer, plywood, engineered panels, finish behaviour, or poorly dried lumber. Use the estimate to design room for movement rather than fighting it.

Formula used

Where:

• board width is measured across the grain
• moisture-content change is the difference between the high and low expected MC%
• flat-sawn boards use the tangential coefficient
• quarter-sawn boards use the radial coefficient
• rift/mixed grain uses an average of radial and tangential coefficients

Worked example

For a 12 inch wide flat-sawn white oak panel with expected seasonal MC from 6% to 12%:

With a 1.25 safety factor, you would plan roughly:

That is enough movement to split a fixed tabletop or bind a drawer if it is not designed for seasonal expansion and contraction.

Species and coefficient assumptions

The calculator uses common practical dimensional-change coefficients. These coefficients represent the approximate fractional change in width for each 1 percentage point change in moisture content.

Examples:

• Black walnut: radial 0.00196, tangential 0.00279
• Black cherry: radial 0.00132, tangential 0.00254
• White oak: radial 0.00200, tangential 0.00375
• Hard maple: radial 0.00171, tangential 0.00354
• Eastern white pine: radial 0.00075, tangential 0.00218

For species not listed, use the custom option or choose a species with similar shrinkage behaviour.

How to use the result

• Use total seasonal movement to understand the full high-to-low swing.
• Use shrink from current if your wood is currently wetter than the target environment.
• Use swell from current if your wood is currently drier than the humid-season environment.
• Use recommended allowance for design clearance, elongated holes, panel grooves, buttons, clips, or tabletop fasteners.
• For drawers and frame-and-panel doors, use the expected movement to avoid binding or buckling.

Assumptions and limitations

• The formula is intended below the fiber saturation point, roughly 28% MC.
• Long-grain movement is ignored because it is usually negligible for furniture-scale projects.
• Finish can slow moisture exchange but does not stop it.
• Wider boards and panels move more in absolute terms.
• Plywood, MDF, veneer panels, and engineered products move differently from solid wood.
• If the predicted movement is large, use joinery that lets the wood move freely.