Construction & DIY · Woodworking
Wood movement calculator.
Pick the species, plainsawn or quartersawn, the width and the moisture content change to see how much the wood grows or shrinks across the grain.
Inputs
Expected width change
Enter a width and two moisture contents.
How much does wood move across the grain?
Wood shrinks most in the direction of the annual rings (tangentially), about half as much across the rings (radially), and only slightly along the grain, according to the USDA Wood Handbook. The Handbook gives each species' average shrinkage from green to ovendry and a method to estimate shrinkage at a moisture content below fiber saturation: Sx = S0 (1 − x / MCfs), where S0 is the species value and 30% is used when the fiber saturation point is not known. Tangential values suit plainsawn boards, radial values suit quartersawn boards, and tangential values are suggested when the ring orientation is unknown or mixed.
Worked example. A 36 in plainsawn white oak top (10.5% tangential) that goes from 6% to 12% moisture content grows by about 0.83 in. The same top quartersawn (5.6% radial) grows by about 0.42 in. Allow for that movement in breadboard ends, table-top fasteners and panel grooves.
Limits. This is a planning estimate. The source data are species averages, and the Handbook notes variability of about 15% and that predicting the shrinkage of an individual piece is impossible. Commercial boards are seldom perfectly plainsawn or quartersawn.
Frequently asked questions
How much will a 36 inch oak tabletop move?
Plainsawn white oak going from 6% to 12% moisture content grows about 0.83 in across the width by the Wood Handbook method; quartersawn grows about 0.42 in.
Does wood move along its length?
Very little. The Wood Handbook gives 0.1% to 0.2% shrinkage from green to ovendry for most species, although reaction wood and juvenile wood can shrink much more.
Which shrinkage value should I use, tangential or radial?
The Wood Handbook says to use tangential values for plainsawn material and radial values for quartersawn, and tangential values when ring orientation is mixed or unknown.
Why is the answer not exact?
The tables are species averages with about 15% variability, and the method assumes shrinkage starts at 30% moisture content and is linear below it. Use the result to leave a sensible gap, not as a measurement.
Sources
Checked
Table 4-3 (shrinkage values of domestic woods, green to ovendry, radial and tangential), Equation 4-9 and the statements on longitudinal shrinkage and variability are from Chapter 4 of the Wood Handbook. The width ratio uses the Handbook relation between shrinkage and moisture content at the two moisture contents you enter. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
Planning estimate for woodworking, not engineering advice. Measure your lumber and leave a margin.