Wood Shrinkage Calculator
Estimate dimensional change when wood gains or loses moisture. Essential for tabletops, panels, and seasonal joints.
Grain orientation:
Shrinkage by Species (green to oven-dry)
| Species | Tangential % | Radial % | T/R Ratio |
|---|---|---|---|
| Red Oak | 8.6 | 4.0 | 2.15 |
| White Oak | 10.5 | 5.6 | 1.88 |
| Hard Maple | 9.9 | 4.8 | 2.06 |
| Cherry | 7.1 | 3.7 | 1.92 |
| Black Walnut | 7.8 | 5.5 | 1.42 |
| White Ash | 7.8 | 4.9 | 1.59 |
| Yellow Poplar | 8.2 | 4.6 | 1.78 |
| E. White Pine | 6.1 | 2.1 | 2.90 |
| S. Yellow Pine | 7.7 | 4.8 | 1.60 |
| W. Red Cedar | 5.0 | 2.4 | 2.08 |
| Douglas Fir | 7.6 | 4.8 | 1.58 |
| Mahogany | 5.1 | 3.7 | 1.38 |
| Teak | 4.0 | 2.6 | 1.54 |
Source: USDA Forest Products Laboratory Wood Handbook, Chapter 4.
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Understanding Wood Movement
Wood is hygroscopic — it absorbs and releases moisture from the air. As moisture content changes, wood dimensions change. This movement is the single biggest cause of cracked tabletops, stuck drawers, and failed glue joints in woodworking.
Movement occurs primarily across the grain, not along it. Tangential shrinkage (flat-sawn boards) is roughly twice radial shrinkage (quarter-sawn). This is why quarter-sawn lumber is prized for stability — it moves about half as much as flat-sawn.
The fiber saturation point (FSP) is approximately 28-30% moisture content for most species. Below FSP, wood shrinks as it dries and swells as it absorbs moisture. Above FSP, dimensional change stops even though the wood can hold more water.
For indoor furniture, expect seasonal MC swings of 4-8% depending on climate and HVAC. A 12-inch flat-sawn red oak tabletop could move over 1/8 inch across its width through the seasons. Always allow for this movement in your joinery.
Wood shrinks and swells as moisture content (MC) changes. The shrinkage percentage is calculated from the species-specific shrinkage coefficient and MC change: shrinkage = coefficient × (MCgreen − MCfinal). Tangential shrinkage (perpendicular to rings, across the face of flatsawn boards) is approximately twice radial shrinkage (perpendicular to growth rings on quartersawn boards).
Example: white oak has a tangential shrinkage coefficient of about 10.5% from green to oven-dry (0% MC). If you buy green lumber at 25% MC and air dry to 12%, the MC change is 13%. Tangential movement = 10.5% × (13/25) ≈ 5.5% across the board width. An 8-inch wide flatsawn white oak board will shrink about 0.44 inches from 25% to 12% MC.
Equilibrium Moisture Content (EMC): wood stabilizes at an MC in equilibrium with surrounding humidity. At 35% relative humidity (common in heated winter homes), EMC ≈ 7%. At 75% RH (summer), EMC ≈ 14%. A panel built to 7% MC will expand by the tangential coefficient × 7% when moved to 75% RH — design joints with this movement in mind.
Quartersawn lumber (growth rings near-perpendicular to face) moves roughly half as much across the face as flatsawn, making it ideal for tabletops, instrument soundboards, and any application requiring dimensional stability.
See also: Board Foot Calculator · Miter Angle Calculator