Wood Movement Gap Calculator

Wood expands and contracts with changes in humidity — this is called seasonal wood movement. If you don't allow for it, the wood will crack, split, buckle or break joints. Expansion gaps allow the wood to move freely. This is especially important for wide panels like tabletops and cabinet panels.

In the UK, indoor wood typically cycles between about 8% MC in winter (when central heating is running) and 12-14% MC in summer. This means a 300mm wide oak board (flat sawn) will move about 4-6mm across its width over the course of a year. Quarter-sawn boards move about half as much.

Flat-sawn boards move in the tangential direction (across the growth rings), which is the maximum movement direction. Quarter-sawn boards move radially (through the growth rings), which is typically about half the tangential movement. This is why quarter-sawn timber is preferred for tabletops and panels.

Attach the tabletop to the base using slotted holes, figure-8 fasteners, or wooden buttons in grooves. These allow the top to expand and contract while staying flat and secure. Never glue or screw a solid wood top rigidly to an apron — it will split.

Plywood moves very little compared to solid wood because the cross-laminated layers cancel out most of the movement. MDF and chipboard also have minimal movement. If your design cannot tolerate seasonal movement, consider using sheet materials for wide panels.