Wood Expansion Calculator — Seasonal Movement

Wood movement depends on species, grain orientation, and moisture content change. A 200mm wide flat-sawn oak board can move about 2.8mm between summer and winter humidity extremes. Quarter-sawn boards move roughly half as much. This calculator gives exact figures.

In the UK, indoor furniture should be at 8-10% moisture content. Wood for unheated spaces should be 12-14%. Outdoor wood stabilises around 16-20%. Allow wood to acclimatise in its final environment for at least 2 weeks before working it.

Flat-sawn (tangential) boards move roughly twice as much as quarter-sawn (radial) boards across their width. Quarter-sawn is more stable because the growth rings run perpendicular to the board face. This is why quarter-sawn is preferred for table tops and wide panels.

Attach the top using elongated screw holes, figure-of-eight clips, or Z-clips that allow the top to expand and contract freely. Never glue a solid top to the apron. Leave 2-3mm expansion gaps at any constraint point. This calculator tells you exactly how much movement to expect.

Plywood is dimensionally stable because the alternating grain directions cancel out most movement. It expands less than 0.1% in either direction. MDF is similarly stable. This is why plywood and MDF are preferred for dimensionally critical applications like jigs and templates.