Wood Movement Calculator
Estimate how much a board will expand or contract across the grain when moisture content changes, using species-specific shrinkage coefficients.
Results
What is it?
Wood is hygroscopic รขโฌโ it absorbs and releases moisture as humidity changes, causing it to swell and shrink across the grain. Understanding this movement is critical in joinery, furniture making, and flooring installation to prevent warping, cracking, and joint failure.
How to use
Enter the board width across the grain and the expected moisture content change (the difference between installation and service condition MC). Enter the shrinkage coefficient for your species and grain orientation (tangential = flat-sawn, radial = quarter-sawn). The result is the total expected movement.
Example scenario
A 150 mm wide flat-sawn oak tabletop installed at 12% MC in a workshop (summer) will reach 8% MC in a centrally heated home in winter. Change = 4 pp. Movement = 150 รโ 0.0369 รโ 4 รขโฐห 22.1 mm รขโฌโ nearly an inch! Slots in the tabletop cleats must accommodate this movement or the top will crack.
Pro tip
Tangential (flat-sawn) movement is roughly twice radial (quarter-sawn) movement, so quarter-sawn boards are dramatically more dimensionally stable. Always account for EMC (Equilibrium Moisture Content) at the installation location รขโฌโ 6-8% for heated interiors, 10-14% for unheated spaces. Leave 1/8 inch expansion gaps per foot of flooring width. Along-grain movement is ~10x less than across-grain.