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.
Wood moves across the grain as humidity changes — a 12″ flat-sawn oak panel can change width by more than ⅛″ between summer and winter. This calculator estimates that movement for 23 common species so you can size breadboard ends, frame-and-panel gaps, and tabletop fasteners before the seasons do it for you.
Design for movement from the start
Members get build plans engineered for seasonal movement, plus workshops on frame-and-panel and tabletop construction.
Longitudinal movement is negligible (about 0.1%). Nearly all seasonal movement is across the grain — tangentially (flat-sawn width) about twice as much as radially (quarter-sawn).
Its growth rings run vertically through the board thickness, so the larger tangential movement happens in the board's thickness rather than its width.
Fasten solid tops with elongated screw slots, figure-8 or Z-clips, and leave the calculated gap in frame-and-panel work. Never glue a wide solid panel rigidly across its grain.