Wood Movement Calculator
Calculate how much wood will expand or contract seasonally.
Essential for furniture makers, flooring installers, and cabinetmakers.
Wood moves — it expands when it absorbs moisture and contracts when it dries. This seasonal movement is one of the most important concepts in woodworking, and ignoring it is the number-one cause of cracked panels, warped tabletops, and failed joints.
The formula for wood movement is: Movement = Width × (MC_change / 100) × Coefficient
Where:
- Width is the board dimension across the grain (perpendicular to the grain is where movement happens — movement along the grain is negligible)
- MC_change is the change in moisture content (MC) in percentage points
- Coefficient is the shrinkage coefficient for that species, typically 0.001 to 0.003 per percentage point of MC change
Movement happens in two directions relative to the growth rings:
- Tangential (parallel to growth rings, flat-sawn lumber): larger movement, coefficient ≈ 0.15–0.25% per 1% MC
- Radial (perpendicular to growth rings, quarter-sawn lumber): smaller movement, coefficient ≈ 0.10–0.15% per 1% MC
This is why quarter-sawn lumber is preferred for tabletops and floors — it moves less and more predictably.
Example: A flat-sawn oak panel, 18 inches wide, going from 6% MC (winter, heated interior) to 12% MC (summer, humid): Movement = 18 × 0.06 × 0.016 (oak tangential) = 0.173 inches ≈ 3/16 inch. You must design the joint or mounting system to allow for this movement.
Common indoor MC range: 6–8% in winter (heated homes), 10–14% in humid summers. Design for the full range in your climate.