Wood movement calculator
How much will a tabletop, a panel or a drawer front grow and shrink across the grain? Pick the species, the width and how the board was sawn, then where its moisture content is now and where it will go. Either one can be given as the air it will live in.
Units
Swells by
0.271 in
about 9/32 in
6% → 12% MC · width becomes 12.271 in
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: White oak swells by the Handbook's own movement equation for this moisture change.
Why these numbers?
The situation
The Wood Handbook gives white oak a tangential dimensional change coefficient of 0.00376 per 1% change in moisture content (Table 13-5).
One source: USDA Forest Products Laboratory, the authority for species properties it measured , sources [1]
What that means
A flatsawn board moves across its width with the tangential value.
From your input: how the board was sawn
So
Between 6% and 14% moisture content the Handbook's Eq. 13-1 applies: change = width × coefficient × (12% − 6%).
Arithmetic: exact by definition , sources [1]
The number
12 in board: +0.271 in.
Arithmetic: exact by definition
Sources
Hardness, weight and uses: White oak wood.
How the movement is worked out
Between 6% and 14% moisture content, wood shrinks and swells in close to a straight line, so the USDA Wood Handbook gives each US species a dimensional change coefficient (Table 13-5): the fraction of its width a board gains or loses for each 1% change in moisture content. The change is width × coefficient × change in moisture content (Eq. 13-1). Outside that range, or for a species with no coefficient, the Handbook works it from the green-to-oven-dry shrinkage instead (Eq. 13-4).
Flatsawn boards move with the tangential figure, quartersawn boards with the radial one, which the Handbook's tables show is smaller for every species. When you aren't sure, the calculator uses the tangential figure, as the Handbook suggests for unknown ring orientation. Air given as temperature and humidity is turned into a moisture content with the Handbook's equation for equilibrium moisture content (Eq. 4-5), the same one behind the EMC calculator.
What it can't tell you
These are averages for clear wood. The Handbook gives shrinkage a coefficient of variation of about 15% (p. 4-11), so one board can move noticeably more or less. Treat the answer as a planning figure.