How much will that panel move? Pick from 100 species, set the seasonal swing, and get the answer in fractions of an inch — with flatsawn and quartersawn side by side.
Board & conditions
Grain
Conditions given as
Typical swings:
Movement estimate
Estimate Figures use species-average shrinkage from the USDA Wood Handbook and the standard shop movement formula. Individual boards vary — leave margin, especially with flatsawn stock.
Want the numbers behind this? Every species has its own page with shrinkage
data, hardness, and workability notes in the wood species library.
Designing for the answer
Wood never stops breathing. Every winter your furniture dries and shrinks; every
summer it swells back. The trick isn’t stopping it — nothing stops it — it’s
knowing the size of the move and leaving room. Three rules cover most projects:
Panels float. A solid panel in a frame sits in grooves with a gap on each side, never glue.
Tops slide. Fasten solid tops with buttons, figure-8 clips, or screws in slotted holes so the top can shift across its width.
Breadboards breathe. Glue only the center of a breadboard end; the outer tenons ride in elongated holes.
The calculator’s guidance lines apply these rules to your exact numbers. When a
swing comes out over ⅛″, take it seriously — that’s the difference between a
door that closes in July and one that doesn’t.
Frequently asked questions
How is wood movement calculated?
The standard shop formula: width × (total shrinkage ÷ 100) × (moisture change ÷ 28). Total shrinkage comes from the USDA Wood Handbook — tangential for flatsawn boards, radial for quartersawn — and 28% is the fiber saturation point, the moisture level below which wood starts changing size. It’s the same method Bruce Hoadley popularized in Understanding Wood.
Why do flatsawn and quartersawn boards move differently?
Wood shrinks roughly twice as much along the growth rings (tangentially) as across them (radially). A flatsawn board’s width runs along the rings, so it gets the big number; a quartersawn board’s width runs across them and gets the small one. That ratio is also why flatsawn boards cup and quartersawn boards mostly don’t.
What moisture content numbers should I use?
Indoors in most of North America, wood settles around 6–7% MC in the heated winter months and 10–12% in humid summers — the calculator’s defaults. Kiln-dried lumber arrives near 8%; air-dried stock and anything from an unheated garage sits closer to 12–14%. If you know the relative humidity instead, switch the toggle and the calculator converts it for you.
Does board length change too?
Barely. Longitudinal shrinkage in normal wood is around 0.1–0.2% from green to ovendry — a 96″ board changes a few hundredths of an inch across a seasonal swing. Movement design is about width and thickness, not length.
Does finish stop wood movement?
No — it only slows it. Film finishes buy weeks, not seasons; the board still reaches the same equilibrium eventually. Build so the wood can move (floating panels, slotted fasteners, breadboard tenons with room) and let the finish smooth the ride rather than fight it.
Shop notes
New tools, when they’re ready
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