Wood Movement Calculator

Expected Movement scales directly with Board Width: the formula multiplies width by the moisture-content change and the species coefficient, so doubling Board Width roughly doubles the movement in inches even though the wood's own shrink-swell rate hasn't changed. That's why a wide glued-up panel needs generous seasonal gaps in a frame-and-panel design while a narrow face frame member barely needs any.

No. Width Change is computed from MC Change and the Coefficient Used only, so a 6-inch board and a 40-inch board subjected to the identical moisture swing report the same percentage change -- Board Width has zero effect on this output. It's the raw-inches Expected Movement output, not Width Change, that scales up with a wider board.

Wood moves roughly twice as much tangentially (flat-sawn, with the growth rings running mostly parallel to the face) as it does radially (quarter-sawn, rings roughly perpendicular to the face), because wood cells are packed differently in the two directions. Setting Grain Direction to Radial instead of Tangential uses the smaller radial coefficient, which is why quarter-sawn lumber is preferred for wide panels and tabletops where minimizing cupping and movement matters most. These per-species radial and tangential coefficients come from Table 13-5 of the USDA Forest Products Laboratory's Wood Handbook (FPL-GTR-282), the standard reference US woodworkers and millwork engineers use for movement allowances.

Alt. Grain Movement recalculates the same board at the same moisture swing but with the opposite grain orientation, so you can compare tangential versus radial movement for identical Board Width and MC Change side by side. It's a quick way to see how much movement allowance you'd recover by choosing quarter-sawn stock instead of flat-sawn (or vice versa) before you commit to a cut.