How Much Will a 6 Inch White Oak Board Move
+0.126" (+3.2 mm)
- Species: White Oak (tangential shrinkage 10.5%)
- Starting width: 6"
- Moisture content: 6% -> 12% (a typical dry-to-humid seasonal swing)
MethodΔD = D x ΔMC x (shrinkage% / 30 / 100)
Your actual humidity swing may be smaller or larger than the 6-12% MC example used here — run your own numbers in the movement calculator.
A 6" wide white oak board will grow about +0.126" (+3.2 mm) across its width from 6% to 12% moisture content — an eighth of an inch, which is easy to dismiss as negligible until it's the width of a single face-frame stile that has to stay flush against its neighbour.
Why this one specifically
Six inches is a common single-board width — a typical stile or rail, a narrow shelf, a single wide floorboard — and it's small enough that this figure often gets ignored entirely on the assumption that "narrow stock doesn't move." White oak's movement scales with width regardless of how narrow the board starts, so an eighth of an inch is real, even if it's the kind of gap a finish coat and a bit of sanding can mostly hide on a single board where a full panel's worth of movement could not be hidden the same way.
What moves the number
Width is the direct lever — a 12" board of the same species moves twice this figure, a 24" panel four times it. Grain orientation matters here too: a quartersawn 6" white oak board would move noticeably less than this flat-sawn figure.