Estimate how much a board will expand or contract across the grain with seasonal humidity changes. Critical for tabletops, panels, and breadboard ends.
Pick the species, grain orientation, board width, and your indoor moisture content swing.
Measure perpendicular to the grain — the dimension that moves.
Typical heated home: 6–8% in winter, 10–12% in summer. Unconditioned shop or coastal climates can swing further.
How to use this:
Shrinkage data from USDA Forest Products Lab Wood Handbook. Formula: ΔW = W × (ΔMC ÷ 30) × shrinkage%. Assumes linear shrinkage below the 30% fiber saturation point.