Wood Shrinkage Calculator
Predict how far a board shrinks as it dries from green to your shop's moisture content — the seasoning math behind stable furniture.
Dry it before you build it
Green wood is cheap and plentiful, but it is still full of water, and it will give that water up — shrinking, and often cupping and checking — until it reaches equilibrium with the air around it. Building before that happens is how tabletops split and drawers seize. Knowing how much a board will shrink tells you how much extra to leave on green stock and how patient to be before final dimensioning.
Once the wood is dry and in service, size finished joinery for the seasons with the Wood Movement Calculator, and size and price your boards with the Board Feet Calculator.
Frequently Asked Questions
What is the fiber saturation point?
The fiber saturation point, around 30 percent moisture content, is the moisture level at which the cell cavities have given up their free water but the cell walls are still full. Above it, drying wood loses water without changing size; below it, water leaves the cell walls and the wood shrinks. That is why this calculator only counts moisture change below about 30 percent — a board drying from 80 percent to 40 percent has not shrunk at all yet.
How is this different from the wood movement calculator?
Shrinkage here is the one-time change as green or wet stock dries down to a stable moisture content — the seasoning that happens before you build. Seasonal wood movement is the smaller, repeating in-and-out that happens afterward as indoor humidity swings. Both use species coefficients, but they answer different questions: this one sizes green boards for drying; the movement tool sizes finished joinery for the seasons.
What moisture content should I dry to?
Aim for the moisture content the finished piece will live at. For furniture in a heated, air-conditioned home that is commonly 6 to 9 percent; in a damp climate or an unheated space it is higher. Building with wood that has already reached its in-service moisture content is the single best way to avoid cracks, open joints, and stuck drawers later. A moisture meter takes the guesswork out.
Does drying only make wood shrink?
No — drying also distorts. As it loses moisture, wood can cup, bow, twist, and check, especially if it dries too fast or unevenly, and flatsawn boards move more than quartersawn. Leave extra width and length on green stock, sticker it with airflow so it dries slowly, and let it acclimate in your shop before final dimensioning. Treat the shrinkage figure as the across-grain allowance, not the whole story.
Estimates from published total-shrinkage values, for the across-grain change below fiber saturation. Real drying also brings cupping and checking — leave extra and let boards acclimate.