How much does a wide board move with the seasons?
A 12-inch plain-sawn white oak board moves about 5/16" across its width between a dry winter and a humid summer. Quarter-sawn moves about half that. Figures by species and cut.
A 12" plain-sawn white oak board moves about 5/16" across its width.
That is 2.8% of its width, swinging between 11 13/16" and 12 3/16" — so a fastener has to allow 3/16" in each direction.
How that is worked out
- Wood moves with moisture content, not with humidity directly. At 25% relative humidity it settles near 5.4% MC; at 70% it reaches 13.1%.
- That is a swing of 7.7 points of moisture content across the year.
- Width × the species coefficient × the swing: 12" × 0.00365 × 7.7 = 5/16". Length along the grain barely changes at all — this is across the width only.
Seasonal movement of a 12" board, 25–70% RH
| Species | Plain sawn | Quarter sawn | Plain sawn, as % of width |
|---|---|---|---|
| Walnut | 1/4" | 3/16" | 2.1% |
| White oak | 5/16" | 3/16" | 2.8% |
| Red oak | 5/16" | 1/8" | 2.8% |
| Hard maple | 5/16" | 1/8" | 2.7% |
| Soft maple | 1/4" | 1/8" | 2.2% |
| Cherry | 1/4" | 1/8" | 1.9% |
| Poplar | 1/4" | 1/8" | 2.2% |
| Ash | 1/4" | 1/8" | 2.1% |
| Hickory | 3/8" | 1/4" | 3.2% |
| Mahogany | 1/4" | 3/16" | 1.8% |
| Sapele | 1/4" | 3/16" | 2.2% |
| White pine | 3/16" | 1/16" | 1.6% |
| Douglas fir | 1/4" | 1/8" | 2.1% |
| Cedar | 3/16" | 1/8" | 1.8% |
Worth knowing
- Coefficients are measured properties from the USDA Wood Handbook. They do not go stale, but they do vary between trees — a species figure is a good bet across a stack and no promise about one board.
- Quarter-sawn moves roughly half as much as plain-sawn in the same species: 3/16" against 5/16" here. That is what you are buying when you pay more for it.
- The humidity range is the thing to get right, and it is about the room rather than the region. A heated house in January is drier than the weather outside it; a workshop over an unheated garage is damper than the house.
- This is movement across the grain. Along the grain wood moves so little that a table top's length is effectively fixed — which is exactly why a breadboard end has to be pegged and slotted rather than glued.
Work out your own numbers
- Wood movement
How far a panel expands and shrinks with the seasons, and what that means for the joint holding it.
- Panel glue-up calculator
How many boards it takes to glue up a target panel width, and how much wider to glue up so the rip lands clean.
Related questions
- How much gap should I leave for wood movement?
- Half the total seasonal swing, in each direction, measured from where the board is now. For a 12" plain-sawn white oak board moving 5/16" over the year that is a bit over 1/8" each way. It matters most where a wide panel meets a fixed frame, where a tabletop is fastened to an apron, and anywhere a run of boards is trapped between two walls.
- Does finishing wood stop it moving?
- No. A film finish slows moisture exchange, so the board reacts to the average of its conditions rather than to last night's rain, but over a season it reaches the same place. Finishing all faces equally is still worth doing — it keeps one face from taking on moisture faster than the other, which is what cups a board.
- Which way does a board cup?
- A plain-sawn board cups away from the heart — the growth rings try to straighten, so the face that was nearer the outside of the tree becomes concave as it dries. Reading the end grain tells you which way a top will go, and it is why alternating the rings in a glue-up is traditional, though matching the grain for looks usually matters more on a well-supported panel.