Wood Movement Calculator
Estimate how far a solid-wood panel expands and contracts across the grain through the year, so your joinery survives winter and summer.
Build so the wood can move
Every solid-wood failure that isn't a bad glue joint is usually wood movement fighting a rigid design. A wide flatsawn panel can move a quarter inch or more between a damp summer and a dry, heated winter. Knowing that number up front tells you how much a panel must float, how far to slot a fastener, and where quartersawn stock earns its keep.
Pair this with the Wood Shrinkage Calculator to see the one-time change as green stock dries, and the Board Feet Calculator to size and price the boards.
Frequently Asked Questions
Why does solid wood move at all?
Wood is hygroscopic: it takes on and gives off moisture with the humidity around it, and swells or shrinks as it does. The movement is almost entirely across the grain — a board barely changes length but noticeably changes width. That seasonal in-and-out is why a tabletop, a raised panel, or a wide drawer front has to be built to move rather than pinned solid.
What is the difference between flatsawn and quartersawn movement?
Wood moves more along the tangential direction (the face of a flatsawn board) than along the radial direction (the face of a quartersawn board) — often more than twice as much. That is why quartersawn stock is prized for wide, stable panels and for anything that has to hold a precise fit, like a plane body or a door frame. This calculator applies the tangential coefficient for flatsawn and the smaller radial one for quartersawn.
What moisture change should I enter?
Enter the swing in the wood's moisture content between the driest and dampest times of year in the environment the piece will live in. In a heated, air-conditioned home that indoor swing is often only a few percent of moisture content, which still translates to meaningful movement on a wide panel; an unheated shop or a humid climate swings more. When in doubt, design for a slightly larger change than you expect.
How do I use the movement figure in a design?
Treat it as the total width change to accommodate. Let solid panels float in grooved frames instead of gluing them in; elongate the screw holes on breadboard ends and tabletop fasteners; and leave a gap on inset doors and drawers. Design so the wood can move freely and the piece survives the seasons; fight the movement and something cracks, racks, or seizes.
Estimates from published movement coefficients. Real movement varies with grain, finish, and how fast humidity swings — treat the figure as a design allowance, not a measurement.