Wood movement (shrinkage) calculator
Enter the board or panel width, species and grain orientation to see how much it moves, for sizing gaps, slots, panel grooves and breadboard ends.
Enter your measurements
- Direction
- Expands (gets wider)
- Width change (nearest 1/16 in)
- 3/16 in
- Panel groove clearance each side (floating panel)
- 1/8 in
- Moisture swing
- 4 percentage points
- Width afterwards
- 12.177 in
- Change as % of width
- 1.48%
12 in × 0.00369 (Red oak, flatsawn) × (10 − 6) = 0.18 in
Groove clearance each side = 3/16 in ÷ 2 + 1/32 in = 1/8 in
- A panel in a frame needs about 1/8 in of room at each edge of its groove to swell into — half the movement plus 1/32 in, a common rule of thumb.
Quick answers for common sizes
| Example | Answer |
|---|---|
| How much a 36 inch red oak tabletop moves | 0.53 in |
| How much a 900 mm walnut tabletop moves | 12.3 mm |
Movement by width (same species and moisture swing)
| Board or panel width | Width change | Change as % of width |
|---|---|---|
| 3 in | 0.0443 in | 1.48% |
| 6 in | 0.0886 in | 1.48% |
| 12 in | 0.18 in | 1.48% |
| 18 in | 0.27 in | 1.48% |
| 24 in | 0.35 in | 1.48% |
| 36 in | 0.53 in | 1.48% |
| 42 in | 0.62 in | 1.48% |
Wood swells and shrinks across its width as its moisture content follows the seasons, while its length barely changes. New to this? Words explained.
The formula
Between about 6% and 14% moisture content, the change in width is close to proportional to the change in moisture. The USDA Wood Handbook publishes a dimensional change coefficient for each species, separately for tangential (flatsawn face) and radial (quartersawn face) movement.
change = width × coefficient × (MC later − MC now) coefficient = change in dimension per 1% moisture change
Example: a 36 in wide flatsawn red oak tabletop going from 6% in winter to 10% in summer moves about 36 × 0.00369 × 4 ≈ 0.53 in — over half an inch. Quartersawn, the same top moves about 0.23 in, and riftsawn about 0.38 in. The full worked example, with fastener and breadboard-end advice, is How much a 36 inch red oak tabletop moves; for a metric build see How much a 900 mm walnut tabletop moves.
Typical coefficients
| Species | Flatsawn (tangential) | Quartersawn (radial) |
|---|---|---|
| Black cherry | 0.00248 | 0.00126 |
| Black walnut | 0.00274 | 0.00190 |
| Hard maple | 0.00353 | 0.00165 |
| Red oak | 0.00369 | 0.00158 |
| White oak | 0.00365 | 0.00180 |
| American beech | 0.00431 | 0.00190 |
| Eastern white pine | 0.00212 | 0.00071 |
| Douglas-fir | 0.00267 | 0.00165 |
| Teak | 0.00186 | 0.00101 |
Riftsawn boards
Between flatsawn and quartersawn sits riftsawn, where the growth rings cross the end of the board at roughly 30 to 60 degrees. The Wood Handbook publishes only the two extremes, radial and tangential; the calculator uses the average of the two for riftsawn stock as a reasonable middle estimate. Real boards drift toward one end or the other depending on the ring angle, and a single wide flatsawn board is often riftsawn near its edges.
What moisture range to plan for
Indoors, wood settles toward an equilibrium moisture content set by the room’s humidity. In much of the US that swings between roughly 6% in heated winter air and 10–12% in humid summers; dry climates stay lower and humid coastal areas higher. A moisture meter on the lumber you are about to use tells you where you are starting from.
If you only know the humidity, switch the calculator to room humidity. It converts each reading to an equilibrium moisture content with the Hailwood–Joy sorption model given in chapter 4 of the USDA Wood Handbook: at 70 °F, 30% RH is roughly 6% MC, 50% about 9%, 65% about 12%. The formula also takes temperature, under More options; warmer air holds wood slightly drier at the same humidity, so at 50% RH wood settles near 9.2% at 70 °F but about 8.9% at 90 °F.
| Relative humidity | 20% | 30% | 40% | 50% | 60% | 70% | 80% |
|---|---|---|---|---|---|---|---|
| Equilibrium MC at 70 °F | 4.5% | 6.2% | 7.7% | 9.2% | 11.0% | 13.1% | 16.0% |
Designing for movement
- Fasten tabletops with buttons, figure-8 fasteners or slotted holes so the top can move across its width.
- Glue breadboard ends only at the center; pin the outer tenons through elongated holes.
- Leave frame-and-panel panels loose in their grooves, with room to expand, and finish them before assembly so bare edges do not show in winter. A common rule of thumb for the gap at each edge of the groove is half the expected movement plus 1/32 in; the calculator shows it whenever the panel will swell.
- Quartersawn stock moves roughly half as much across its width as flatsawn — worth it for wide panels and drawer fronts.
A finish does not stop any of this. It slows how fast moisture gets in and out, which is why both faces of a top should get the same treatment — How much polyurethane for a dining table works out how much that takes.
What you’ll need
- Wood moisture meterMid-range price
Tells you whether lumber is dry enough to build with and firewood dry enough to burn. Readings vary by species — check the meter’s correction settings.
See options on Amazon (opens in a new tab) - Tabletop fasteners (figure-8 or Z-clips)Budget price
Hold a solid-wood top to its apron while letting it expand and shrink across the grain.
See options on Amazon (opens in a new tab) - Digital calipersBudget price
For measuring actual board and plywood thickness to the thousandth — useful for sizing dadoes and checking planed stock.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much does a solid wood tabletop move?
It depends on width, species, cut and moisture swing. A 36 in flatsawn red oak top moving from 6% to 10% moisture changes by about ½ in across its width (How much a 36 inch red oak tabletop moves); a cherry top of the same width about ⅜ in.
Does wood expand along its length?
Very little — usually around 0.1–0.2% from green to oven-dry for normal wood, which is negligible for most furniture. The movement you design for is across the width and thickness.
What moisture content does wood reach indoors?
It settles to an equilibrium set by the air. At about 70 °F, 30% relative humidity gives roughly 6% moisture content, 50% gives about 9%, and 60% about 11% (USDA Wood Handbook). Choose the humidity option in the calculator to use your own hygrometer readings.
How much clearance does a floating panel need in its groove?
Half the panel’s expected movement at each edge, plus a little: a common rule of thumb is movement ÷ 2 + 1/32 in. A 12 in flatsawn red oak panel built at 6% that could reach 10% moves about 0.18 in, so each edge needs about 1/8 in of room. Glue-up in a humid season needs less, because the panel will mostly shrink.
Why does quartersawn wood move less?
Wood shrinks roughly twice as much tangentially (along the growth rings) as radially (across them). A quartersawn board’s width runs radially, so it moves less across the face: a 900 mm walnut top moves about 12.3 mm flatsawn but 8.55 mm quartersawn (How much a 900 mm walnut tabletop moves).
Related guides
Sources
- USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-282), Chapter 4: Moisture relations and physical properties of wood (opens in a new tab) — Equilibrium moisture content and the Hailwood–Joy sorption model this calculator uses in humidity mode; shrinkage by species.
- USDA Forest Products Laboratory, Wood Handbook: Wood as an Engineering Material (FPL-GTR-282, 2021) (opens in a new tab) — Full handbook, including the dimensional change coefficients (per 1% moisture change, radial and tangential) used here.
- The Wood Database (Eric Meier) (opens in a new tab) — Species shrinkage figures for cross-checking.