Wood Shrinkage Calculator

It depends on the width, the species, the saw cut, and how far the moisture content moves. A 10 inch flatsawn oak board drying from 12 percent to 7 percent shrinks about 0.18 inch across its width, while a quartersawn board the same size moves roughly half that.

Each species and cut maps to a dimensional change coefficient, the fractional change in width per 1 percent change in moisture. Flatsawn boards use the larger tangential value and quartersawn boards use the smaller radial value. These are typical published figures, so treat the output as a planning estimate rather than a guarantee for one specific board.

Quartersawn boards expose the radial face, and wood shrinks less radially than tangentially. For every species here the quartersawn coefficient is close to half the flatsawn one, which is why quartersawn stock is prized for wide, stable panels and instrument tops.

It is the moisture content, near 28 percent, below which wood begins to shrink and swell. Above it the extra water sits free in the cell cavities and does not change the size of the board. The tool clamps both moisture readings to 28 percent, so entering 40 percent is treated the same as 28.

Yes. If the target moisture is higher than the start moisture the board gains water, so the change is negative and the panel gets wider. The result then reads Swells rather than Shrinks and the final width is larger than the starting width.

Enter the width, the dimension that moves the most across the grain. Length along the grain barely changes and is not modeled here, so use the tool for board width, panel width, or the total width of several glued boards.

Let wide panels float in their grooves, drill oversized or slotted holes so a solid top can slide across a fixed base, and acclimate lumber in the room where it will live before you build. Sizing the expansion gap to the calculated movement keeps panels from cracking or bowing.

No. The calculation runs entirely in your browser using fixed coefficients, so nothing about your project is uploaded or stored on a server.

The five species cover common furniture and construction woods, but the underlying formula only needs a coefficient. The API accepts a custom shrinkageCoefficient value, so you can plug in a published figure for any species and get the same math.