Wood swells in humid summers and shrinks in dry, heated winters, across the grain but hardly at all along it. This calculator predicts that change for a board or glued-up panel from its width, species, grain orientation and the moisture contents it moves between, using the shrinkage values and equation published in the USDA Wood Handbook. Use it to size floating panels, breadboard ends, tabletop fastener slots and drawer clearances.
Wood movement calculator
How it works
The Wood Handbook gives each species a total shrinkage from green to oven-dry, radially and tangentially, and treats movement as linear below the fibre saturation point (about 30% moisture content). Its dimensional-change equation is:
- Change = width × (final MC − initial MC) ÷ (30 × 100 ÷ S − 30 + initial MC)
- S = the species’ green-to-oven-dry shrinkage in percent: tangential for flatsawn boards, radial for quartersawn, the average for rift or mixed grain
A negative result is shrinkage, a positive one is swelling. The rule of thumb that wood moves about 1% for every 4% change in moisture content (American Wood Council) comes from the same table.
Worked example
A 12 in wide flatsawn red oak panel bought at 12% moisture content and taken into a heated house that brings it to 6%:
- Units: Inches and feet
- Species: Red oak (northern)
- Grain orientation: Flatsawn (tangential, most movement)
- Width across the grain: 12 in
- Moisture content now: 12%
- Moisture content later: 6%
The calculator gives:
- Change in width: -0.218 in (7/32") (shrinks)
- New width: 11.782 in (11-25/32")
- Change as a percentage: -1.81%
- Per 1% change in moisture: 0.036 in (1/32") for this width
- Shrinkage used: Red oak (northern): tangential 8.6% green to ovendry
The panel shrinks about 7/32 in (0.218 in). Quartersawn red oak would move less than half that (radial shrinkage 4.0% against tangential 8.6%). A 36 in wide tabletop of the same stock would move about 5/8 in, which is why tops are fastened with slotted holes or buttons rather than screwed tight.
Shrinkage values used (percent, green to oven-dry)
| Species | Radial | Tangential |
|---|---|---|
| African padauk | 3.1 | 5 |
| American beech | 5.5 | 11.9 |
| American elm | 4.2 | 9.5 |
| Bald cypress | 3.8 | 6.2 |
| Balsam fir | 2.9 | 6.9 |
| Basswood | 6.6 | 9.3 |
| Black cherry | 3.7 | 7.1 |
| Black locust | 4.6 | 7.2 |
| Black walnut | 5.5 | 7.8 |
| Bubinga | 6 | 8.2 |
| Butternut | 3.4 | 6.4 |
| Douglas-fir (coast) | 4.8 | 7.6 |
| Eastern cottonwood | 3.9 | 9.2 |
| Eastern hemlock | 3 | 6.8 |
| Eastern red cedar (aromatic) | 3.1 | 4.7 |
| Eastern white pine | 2.1 | 6.1 |
| Engelmann spruce | 3.8 | 7.1 |
| Hard (sugar) maple | 4.8 | 9.9 |
| Hickory (shagbark) | 7 | 10.5 |
| Ipe | 5.5 | 7.1 |
| Jatoba (Brazilian cherry) | 4.2 | 8 |
| Lodgepole pine | 4.3 | 6.7 |
| Mahogany (Honduran) | 2.9 | 4.3 |
| Pecan | 4.9 | 8.9 |
| Ponderosa pine | 3.9 | 6.2 |
| Purpleheart | 3.8 | 6.4 |
| Quaking aspen | 3.5 | 6.7 |
| Red alder | 4.4 | 7.3 |
| Red oak (northern) | 4 | 8.6 |
| Redwood | 2.4 | 4.7 |
| Sapele | 5.2 | 7.2 |
| Sitka spruce | 4.3 | 7.5 |
| Soft (red) maple | 4 | 8.2 |
| Southern yellow pine (loblolly) | 4.8 | 7.4 |
| Sugar pine | 2.9 | 5.6 |
| Sweetgum | 5.3 | 10.2 |
| Sycamore | 5 | 8.4 |
| Teak | 2.6 | 5.3 |
| Wenge | 4.8 | 8.3 |
| Western hemlock | 4.2 | 7.8 |
| Western larch | 4.5 | 9.1 |
| Western red cedar | 2.4 | 5 |
| White ash | 4.9 | 7.8 |
| White fir | 3.3 | 7 |
| White oak | 5.6 | 10.5 |
| White spruce | 4.7 | 8.2 |
| Yellow birch | 7.3 | 9.5 |
| Yellow poplar | 4.6 | 8.2 |
Notes and limits
- Above about 30% moisture content (green wood) the size does not change, so the calculator only accepts 0 to 30%.
- Indoor wood in most of North America swings between roughly 6% (winter heating) and 12% (humid summer); coastal and unconditioned spaces run higher. A pin meter tells you where your stock is now.
- The table values are species averages. Individual boards vary, and growth-ring angle in between flat and quarter gives movement in between.
- Length along the grain changes only about 0.1 to 0.2% from green to dry, which is why frame-and-panel construction lets the panel float in a fixed frame.
- Plywood and MDF move far less across the sheet than solid wood; this calculator is for solid lumber.
Frequently asked questions
How much does wood move with humidity?
Roughly 1% of its width for every 4% change in moisture content across the grain, more for flatsawn than quartersawn. A 12 in flatsawn red oak board going from 12% to 6% moisture shrinks about 7/32 in.
Which direction does wood shrink the most?
Tangentially, around the growth rings, so flatsawn boards move most across their width. Radial movement (across quartersawn faces) is about half as much, and lengthwise movement is negligible.
What moisture content should furniture wood be?
Around 6 to 8% for wood that will live in a heated home, matching the equilibrium the room reaches. Buying at 12% and building right away invites cracks and gaps later.
How much gap should I leave for a floating panel?
Use the calculator with the panel width and the driest condition it will see. Leave at least that much total clearance, split between the two grooves, and pin the panel only at its centre.
Does finish stop wood movement?
No. Film finishes slow the exchange of moisture, which evens out short swings, but the wood still reaches equilibrium with the room over weeks.
Sources
- USDA Forest Products Laboratory, Wood Handbook: Wood as an Engineering Material (FPL-GTR-282, 2021), Chapter 4: Table 4-3 shrinkage values of domestic and imported woods, and the dimensional-change equation for moisture contents below fibre saturation
- The Wood Database, "Dimensional Shrinkage" and the species pages consulted for radial and tangential shrinkage and modulus of elasticity (tabulated from the Wood Handbook)
- American Wood Council, "Where can I find information on wood shrinkage?" (about 1% dimension change per 4% moisture change across the grain)
Last reviewed: 26 September 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.
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