Wood Movement Calculator

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.