Wood Movement Calculator
Wood swells and shrinks across the grain as its moisture content changes with the seasons. Enter a board and a moisture swing to see how much room to leave in tabletops, panels, flooring and decking.
Species & grain
Idealized flatsawn width uses tangential shrinkage; quartersawn width uses radial shrinkage. Actual ring angles and the species-specific ratio vary.
Board size
Moisture content change
Estimated movement
+0.270"
width change ≈ 9/32" · +2.25%
Simplified linear estimate from the listed total-shrinkage inputs, assuming a 28% fiber-saturation point. Reference inputs and actual boards vary; no universal ±25% tolerance or installation approval is established.
Equilibrium moisture content (70°F)
Model estimates at a constant 70°F; these are not measured stock moisture or universal installation targets. The condition presets are illustrative assumptions, not delivery certificates.
20% RH
4.5% MC
30% RH
6.2% MC
40% RH
7.7% MC
50% RH
9.2% MC
60% RH
11% MC
70% RH
13.1% MC
80% RH
16% MC
90% RH
20.5% MC
Lumberama source-based guidance · Updated October 1, 2026. No independent field measurements or installation approval are claimed.
Choose the service environment, not a state-wide target
Use the conditions the finished assembly will actually see: a heated room, conditioned kitchen, unconditioned workshop and covered porch may differ within the same city. Track temperature and relative humidity over representative dry and humid seasons. A single weather-app reading is neither the indoor condition nor evidence of a stable yearly target.
Measure a representative set of boards
Check the meter against its manufacturer’s procedure, apply its actual species or specific-gravity setting and follow temperature and measuring-depth instructions. Avoid treating one surface reading as the whole load. Sample different boards, positions and appropriate depths, and record the date, instrument, settings, room conditions and readings. Investigate outliers, recent wetting and differences between surface and interior moisture.
Acclimation is a condition, not a countdown
Thicker stock, restricted airflow, coatings, packaging and moisture gradients can change the response. A fixed one- or two-week rule cannot prove readiness. Maintain the expected service conditions, support and stack the product as instructed, and repeat measurements until the relevant product, substrate and installation requirements are met. Close agreement with estimated EMC is useful context, not permission to install.
Check flooring, substrate and adhesive requirements separately
For flooring, compare the flooring and subfloor readings using the flooring manufacturer’s accepted limits and method. Concrete requires its own specified assessment; a wood meter reading does not establish slab readiness. For coatings and adhesives, follow their substrate and moisture requirements. Resolve conflicts with the responsible manufacturer or installer rather than averaging incompatible acceptance limits.
Allow movement in the assembly
Wood moves mainly across the grain. Use the expected seasonal moisture range and actual board orientation to plan panel clearances, slotted attachments and suitable fasteners. A rigid cross-grain connection can restrain movement and cause damage. Do not interpret a generic movement estimate as an expansion-gap instruction for a proprietary flooring or decking product.
Worked movement example and model limits
With this calculator’s white-oak tangential shrinkage input of 10.5%, a 12-inch width, moisture increasing from 6% to 12%, and the assumed 28% fiber-saturation point, the linear estimate is 12 × 0.105 × 6 ÷ 28 = 0.270 inch. This is an approximate total change across that moisture interval, not automatically a 0.270-inch gap at each end. Growth-ring angle, actual species, board variability and attachment geometry affect the allowance.
Sources and method
EMC uses the Hailwood–Horrobin two-hydrate equation with Fahrenheit coefficients. Movement uses a simplified linear approximation below an assumed 28% fiber-saturation point. Neither predicts acclimation time, engineering capacity or batch acceptance.