How to use this calculator
Start by selecting the wood species you are working with. The calculator includes over 20 common domestic and exotic hardwoods, each with published tangential and radial shrinkage coefficients from the USDA Forest Products Laboratory.
Next, choose the grain orientation. Flatsawn is the most common cut and has the most movement across the width. Quartersawn moves roughly half as much. Rift sawn falls in between. If you are not sure which cut you have, look at the end grain: flatsawn boards show curved cathedral grain on the face, while quartersawn boards show straight parallel lines.
Enter the board width in inches. For a glued-up panel or tabletop, enter the total width of the panel across the grain, not the width of individual boards. Wood movement accumulates across the full width.
Finally, enter the moisture content at the time of building (typically 6% to 8% for kiln dried lumber) and the lowest and highest moisture content you expect the piece to reach in its final environment. If you are not sure, click the climate reference guide to see typical ranges for different regions. The calculator will show you the expected shrinkage, expansion, and total seasonal swing in both decimal inches and fractions.
Why wood movement matters
Wood is hygroscopic, meaning it absorbs and releases moisture from the air. As it absorbs moisture, the wood fibers swell and the board gets wider. As it dries out, the fibers contract and the board shrinks. This cycle repeats every year with the seasons and never stops, even in furniture that is decades old.
Ignoring wood movement is one of the most common mistakes in woodworking. A tabletop screwed rigidly to a frame will crack. A drawer built too tight will stick in summer. A cabinet door with no room in the frame will buckle. Understanding how much your wood will move lets you design joints and clearances that accommodate the movement instead of fighting it.
Grain orientation and movement
The direction of the growth rings relative to the face of the board determines how much it moves. Tangential movement (parallel to the growth rings) is always greater than radial movement (perpendicular to the growth rings), usually by a factor of about two to one.
In a flatsawn board, the wide face is tangent to the growth rings, so the width changes the most. In a quartersawn board, the growth rings run perpendicular to the face, so the width changes much less. This is why quartersawn lumber is prized for tabletops, panel doors, and any application where stability matters. It costs more because the sawing pattern yields less usable wood from each log, but the improved stability is worth it for critical components.
Frequently asked questions
How much does wood shrink and expand?
It depends on species, grain cut, and moisture change. A 12 inch wide flatsawn red oak board might move about 1/8 inch across a typical seasonal swing. Quartersawn moves roughly half that. Stable species like teak and mahogany move much less than species like beech and hickory.
What is the difference between flatsawn and quartersawn?
Flatsawn boards have growth rings roughly parallel to the face, showing cathedral grain. Quartersawn boards have rings perpendicular to the face, showing straight parallel lines. Quartersawn moves about half as much across the width, making it more stable for tabletops and doors.
What moisture content should kiln dried wood be?
Kiln dried hardwood for indoor furniture should be 6% to 8% MC. This matches the equilibrium of a typical climate controlled home. Always verify with a moisture meter before building. Lumber above 10% is not fully dried and will continue shrinking indoors.
Does wood expand in summer or winter?
Wood expands in summer when humidity is higher and shrinks in winter when heating dries the air. This seasonal cycle is why woodworkers design joints and attachments that allow movement rather than resisting it. The total swing between the driest and most humid conditions is the number you need to plan for.