Wood Shrinkage Calculator
Predict board width change between two moisture contents using USDA Wood Handbook shrinkage coefficients.
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What this tool does
Predict board width change between two moisture contents using USDA Wood Handbook shrinkage coefficients. Coefficients are USDA Wood Handbook total shrinkage values (green to oven-dry). The linear approximation applies between about 6% and 20% MC for most species; movement reverses (swelling) when final MC is higher. Length (longitudinal) movement is negligible and not modelled.
How to use the Wood Shrinkage Calculator
- Enter or select wood species (usda wood handbook).
- Enter or select board cut / direction.
- Enter or select board width at starting moisture in in.
- Enter or select starting moisture content (%).
- Enter or select final moisture content (%).
- Read the calculated result; change any measurement to compare alternatives.
Formula
width change ≈ width × total shrinkage% × (MCfrom − MCto) / 30 — shrinkage below the ~30% fibre saturation point is approximately linear with moisture change (USDA Wood Handbook method)
- speciesS
- Wood species (USDA Wood Handbook)
- cut
- Board cut / direction
- boardWidth
- Board width at starting moisture (in, before metric conversion)
- mcFrom
- Starting moisture content (%)
- mcTo
- Final moisture content (%)
Coefficients are USDA Wood Handbook total shrinkage values (green to oven-dry). The linear approximation applies between about 6% and 20% MC for most species; movement reverses (swelling) when final MC is higher. Length (longitudinal) movement is negligible and not modelled.
Worked example
For wood shrinkage calculator, the following measurements illustrate the exact method: Wood species (USDA Wood Handbook): redOak; Board cut / direction: tangential; Board width at starting moisture: 10; Starting moisture content (%): 15; Final moisture content (%): 8.
Inputs
- Wood species (USDA Wood Handbook)Red oak (northern) (R 4% / T 8.6%)
- Board cut / directionFlat-sawn — width moves tangentially
- Board width at starting moisture10 in
- Starting moisture content (%)15
- Final moisture content (%)8
Result
- Width change0.2 in
- Final width9.8 in
- Movement per inch of width0.02 in
- DirectionShrinks as it dries
Total shrinkage, green → oven-dry (USDA Wood Handbook)
| Species | Radial (%) | Tangential (%) |
|---|---|---|
| Red oak (northern) | 4 | 8.6 |
| White oak | 5.6 | 10.5 |
| Hard maple (sugar) | 4.8 | 9.9 |
| Black walnut | 5.5 | 7.8 |
| Black cherry | 3.7 | 7.1 |
| Douglas fir (coast) | 4.8 | 7.6 |
| Loblolly pine | 4.8 | 7.4 |
| Eastern white pine | 2.1 | 6.1 |
| Western red cedar | 2.4 | 5 |
| White ash | 4.9 | 7.8 |
| Shagbark hickory | 7 | 10.5 |
| Teak | 2.6 | 5.3 |
Results explained
- Width change
- Width change from the formula above, expressed in in before metric conversion. Coefficients are USDA Wood Handbook total shrinkage values (green to oven-dry). The linear approximation applies between about 6% and 20% MC for most species; movement reverses (swelling) when final MC is higher. Length (longitudinal) movement is negligible and not modelled.
- Final width
- Final width from the formula above, expressed in in before metric conversion. Coefficients are USDA Wood Handbook total shrinkage values (green to oven-dry). The linear approximation applies between about 6% and 20% MC for most species; movement reverses (swelling) when final MC is higher. Length (longitudinal) movement is negligible and not modelled.
- Movement per inch of width
- Movement per inch of width from the formula above, expressed in in before metric conversion. Coefficients are USDA Wood Handbook total shrinkage values (green to oven-dry). The linear approximation applies between about 6% and 20% MC for most species; movement reverses (swelling) when final MC is higher. Length (longitudinal) movement is negligible and not modelled.
- Direction
- Direction from the formula above. Coefficients are USDA Wood Handbook total shrinkage values (green to oven-dry). The linear approximation applies between about 6% and 20% MC for most species; movement reverses (swelling) when final MC is higher. Length (longitudinal) movement is negligible and not modelled.
Frequently asked questions
Example: a 10 in flat-sawn red oak board going from 15% to 8% moisture moves 10 × 8.6% × 7/30 ≈ 0.20 in narrower. Quarter-sawn, the same board moves only about 0.09 in (radial coefficient).
Wood shrinks roughly twice as much tangentially (along the growth rings) as radially (across them) — the USDA table shows it for every species. Flat-sawn board width lies mostly in the tangential direction.
About 28–30% moisture content. Above it, wood loses only free water from cell cavities and does not shrink; all dimensional change happens below it, which is why the formula divides the moisture change by 30.
Let wide panels float: breadboard ends with elongated slots, tabletop buttons or figure-8 fasteners, frame-and-panel construction, and gaps sized from this calculator for your species and expected seasonal MC swing (often 6–8 points indoors).
Almost never measurably — longitudinal shrinkage is typically 0.1–0.2% total green-to-dry, so a 8 ft board changes length by under a fifth of an inch worst case and usually far less. Width and thickness are where movement lives.