Wood Shrinkage Calculator

In short Wood moves with moisture, and it moves in two directions by very different amounts. This works out how much a board will shrink or swell across its width as its moisture content changes, using the standard linear approximation below fibre saturation. The single most useful fact here is the ratio: almost every species moves roughly twice as much TANGENTIALLY, around the growth rings, as it does RADIALLY, out from the centre. That is exactly why quartersawn timber is prized — its face is oriented so that the smaller radial movement is what shows across the width. This page computes that ratio from the species figures rather than asserting it. The second useful fact is the ceiling. Wood does not move at all above the fibre saturation point, around 28% moisture content, because water above that sits free in the cell cavities rather than in the cell walls. Green timber can lose a great deal of weight before it starts to change size at all. What to do about it is simple to say and easy to forget: you cannot stop the movement, so let it happen. Panels float in their frames, breadboard ends are slotted rather than glued across, and tabletops are fixed with buttons or slotted fasteners. A board glued solid at both ends will split instead of moving.