Woodworking calculator
Wood Movement Calculator
Wood is hygroscopic: it gives up and takes on moisture with the seasons, and shrinks or swells across the grain as it does. Choose a species, say whether the board is flat-sawn or quarter-sawn, enter its width and the moisture content now and later, and this calculator estimates how much it will move, the number you need to leave room for in joinery and panels.
How it works
Below the fiber saturation point, around 28 to 30 percent moisture content, wood shrinks and swells roughly in proportion to how much its moisture content changes. The dimensional change equals the starting width times the change in moisture content times a dimensional change coefficient for the species and direction.
Direction matters because wood moves about twice as much tangentially as radially. Flat-sawn boards move mostly tangentially, the larger figure, while quarter-sawn boards move mostly radially and stay more stable, which is one reason quarter-sawn stock is prized for wide panels and door frames. This tool uses grounded tangential and radial coefficients from the published wood movement tables and picks the right one from the grain orientation you select.
Above the fiber saturation point the extra water sits free in the cell cavities and causes no further dimensional change, so the calculator caps moisture inputs there. The result is the expected change in width: plan gaps, floating panels, and fastening so that this much seasonal movement is allowed to happen without splitting or buckling.
Worked example
A 12 in wide flat-sawn Red Oak board drying from 12% to 7% moisture content moves about 0.221 in (narrower), finishing near 11.779 in.
Movement coefficients by species
Movement depends on the tangential (CT) and radial (CR) dimensional change coefficients. These grounded values come from the published wood movement tables; higher numbers move more.
| Species / material | Type | MOE (psi) | Specific gravity | Janka (lbf) | Movement CT / CR |
|---|---|---|---|---|---|
| American Beech | hardwood | 1,720,000 | 0.72 | 1,300 | 0.00431 / 0.00190 |
| Bald Cypress | softwood | 1,440,000 | 0.51 | 510 | 0.00216 / 0.00130 |
| Black Cherry | hardwood | 1,490,000 | 0.56 | 950 | 0.00248 / 0.00126 |
| Black Walnut | hardwood | 1,680,000 | 0.61 | 1,010 | 0.00274 / 0.00190 |
| Douglas-Fir | softwood | 1,765,000 | 0.51 | 620 | 0.00267 / 0.00165 |
| Eastern Redcedar | softwood | 880,000 | 0.53 | 900 | 0.00162 / 0.00106 |
| Eastern White Pine | softwood | 1,240,000 | 0.40 | 380 | 0.00212 / 0.00071 |
| Hard Maple | hardwood | 1,830,000 | 0.71 | 1,450 | 0.00353 / 0.00165 |
| Loblolly Pine | softwood | 1,790,000 | 0.57 | 690 | 0.00263 / 0.00176 |
| Lodgepole Pine | softwood | 1,340,000 | 0.47 | 480 | 0.00234 / 0.00148 |
| Red Alder | hardwood | 1,380,000 | 0.45 | 590 | 0.00256 / 0.00151 |
| Red Maple | hardwood | 1,640,000 | 0.61 | 950 | 0.00289 / 0.00137 |
| Red Oak | hardwood | 1,761,000 | 0.70 | 1,220 | 0.00369 / 0.00158 |
| Redwood | softwood | 1,220,000 | 0.42 | 450 | 0.00229 / 0.00101 |
| Shagbark Hickory | hardwood | 2,160,000 | 0.80 | 1,880 | 0.00411 / 0.00259 |
| Silver Maple | hardwood | 1,140,000 | 0.53 | 700 | 0.00252 / 0.00102 |
| Sitka Spruce | softwood | 1,600,000 | 0.42 | 510 | 0.00263 / 0.00148 |
| Sugar Pine | softwood | 1,190,000 | 0.40 | 380 | 0.00194 / 0.00099 |
| White Ash | hardwood | 1,740,000 | 0.67 | 1,320 | 0.00274 / 0.00169 |
| White Oak | hardwood | 1,762,000 | 0.75 | 1,350 | 0.00365 / 0.00180 |
| White Spruce | softwood | 1,315,000 | 0.43 | 480 | 0.00274 / 0.00130 |
| Yellow Birch | hardwood | 2,010,000 | 0.69 | 1,260 | 0.00338 / 0.00256 |
| Yellow Poplar | hardwood | 1,580,000 | 0.46 | 540 | 0.00289 / 0.00158 |
Frequently asked questions
What causes wood to move?
Wood absorbs and releases moisture as humidity changes through the seasons. Below the fiber saturation point it shrinks as it dries and swells as it takes on moisture, almost entirely across the grain.
What is the difference between flat-sawn and quarter-sawn movement?
Flat-sawn boards move tangentially and change width about twice as much as quarter-sawn boards, which move radially. Quarter-sawn stock is more dimensionally stable, useful for wide panels and frames.
What moisture content should I use?
Use the moisture content the wood is at now and the value it will reach in service. Interior wood often cycles between roughly 6 and 9 percent, and a meter or a kiln target gives a reliable figure.
Why does movement stop above 30 percent moisture?
At the fiber saturation point, near 28 to 30 percent, the cell walls are full and additional water is stored loose in the cavities. That free water adds weight but causes no further shrinking or swelling.
How do I use the result in a project?
Leave room for the predicted change: float wide panels in grooves, slot screw holes in breadboard ends and tabletop fasteners, and avoid gluing cross-grain so seasonal movement does not crack the work.
Related calculators
Sources
These calculators are for planning and estimation. Engineering results (shelf sag, wood movement) use published average material properties; real boards vary by grade, grain, moisture and defects. Verify load-bearing designs with a professional.