Wood Movement Calculator
Quartersawn moves half as much — on average. On white pine it saves 2.9x and on birch only 1.3x, so the rule is per species.
"Quartersawn moves half as much" — true on average, wrong for your board
Across twelve common species the tangential-to-radial ratio averages 1.84, so the rule is a fair summary. But the spread is what actually matters when you are choosing boards.
| Species | Tangential | Radial | Quartersawn saves |
|---|---|---|---|
| Pine, eastern white | 6.1% | 2.1% | 2.90× |
| Beech | 11.9% | 5.5% | 2.16× |
| Oak, red | 8.6% | 4% | 2.15× |
| Maple, hard | 9.9% | 4.8% | 2.06× |
| Cherry, black | 7.1% | 3.7% | 1.92× |
| Oak, white | 10.5% | 5.6% | 1.88× |
| Poplar, yellow | 8.2% | 4.6% | 1.78× |
| Ash, white | 7.8% | 4.9% | 1.59× |
| Douglas fir | 7.6% | 4.8% | 1.58× |
| Walnut, black | 7.8% | 5.5% | 1.42× |
| Mahogany, Honduran | 5.1% | 3.7% | 1.38× |
| Birch, yellow | 9.5% | 7.3% | 1.30× |
On eastern white pine, quartersawn moves 2.9 times less and is transformative. On yellow birch it is 1.3 and barely worth paying for. Choosing quartersawn for stability is a decision to make per species, not by the rule.
What is verified here, and what is not
The moisture model is the Hailwood-Horrobin equation from the Wood Handbook. It has not been checked against a printed equilibrium moisture content table — two recollections of that table disagreed by more than a percentage point and there was no source to settle it, so no claim of table agreement is made anywhere on this page.
What has been checked is the physics, which is the better test. The model converges on 28.7% at saturation, and the fibre saturation point of wood is conventionally 28 to 30% — nothing in the equation mentions that number, so landing there is independent evidence the constants are right. It also goes to 0.03% in bone dry air, rises monotonically with humidity at every temperature, and falls monotonically with temperature at every humidity, across 1,770 sample points.
A moisture meter is the authority. This is a planning model, and the shrinkage figures are published reference values that real boards vary from.
Notes
- Wood moves across the grain, essentially not along it. Length change is negligible, which is why a frame-and-panel door works: the panel floats and the frame does not have to.
- Above fibre saturation nothing moves. Wood only shrinks and swells as water leaves and enters the cell walls, so the swing is clamped at that point.
- Acclimatise before you build. Stack the wood in the room it will live in for a couple of weeks. Building to a number and letting the wood arrive at it afterwards is how panels split.
- Design for the movement rather than against it. Floating panels, elongated screw holes, breadboard ends pinned only at the centre — the traditional details all exist because this number is not zero.
How to use
- Pick the species and how the board was cut.
- Enter the width and the humidity range your room actually swings through.
- Read the movement, and compare the three cuts before buying.
- Acclimatise the wood in the room before building to any of it.
Frequently asked questions
How much does wood move seasonally?
It depends on the species, the cut and the humidity swing, but a 12-inch flatsawn red oak panel moves roughly a quarter of an inch between a dry heated winter and a humid summer. That is more than enough to split a panel glued solid into a frame.
Does quartersawn really move half as much?
On average, yes — across twelve common species the tangential-to-radial ratio averages 1.84. But the spread is what matters for the board in front of you: eastern white pine is 2.90 and yellow birch is 1.30. On pine quartersawn is transformative; on birch it barely helps.
Why does wood move more in one direction?
Because of how the cell structure is arranged around the growth rings. Tangential movement — around the rings — always exceeds radial movement across them, in every species. Which direction that ends up being across your board is decided by how it was sawn.
What is equilibrium moisture content?
The moisture level wood settles at for a given temperature and humidity. It is what drives all movement: wood shrinks and swells as water enters and leaves the cell walls, and stops moving entirely above the fibre saturation point of about 28%.
Is this calculator accurate?
It is a planning model, and the page is explicit about what has been checked. The moisture equation was not verified against a printed table — two recollections of that table disagreed and there was no source to settle it. What was verified is the physics: it converges on 28.7% at saturation, which is the fibre saturation point it was never told, and it is monotone in both humidity and temperature across 1,770 sample points.
Does wood move along its length?
Essentially not — longitudinal movement is negligible compared with across the grain. That asymmetry is the reason frame-and-panel construction exists: the panel floats and moves, and the frame around it does not have to.
Should I acclimatise wood before building?
Yes. Stack it in the room it will live in for a couple of weeks so it reaches equilibrium there. Building to a calculated number and letting the wood arrive at it afterwards is exactly how panels split and doors stick.
How do I design around movement?
Let it happen somewhere harmless. Floating panels in grooves, elongated screw holes on tabletop fasteners, breadboard ends pinned only at the centre — every traditional detail of that kind exists because this number is not zero.
Does this send anything anywhere?
No. Everything is calculated in your browser and nothing is stored or uploaded.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.