Project notes
Understand this estimate
A supplied movement coefficient estimates dimensional change from a moisture-content change. Coefficient meaning depends on species, grain direction and source.
How to use the calculator
Measure the starting dimension
Measure along the grain direction that the coefficient describes.
Inputs Starting dimension
Enter a sourced coefficient and moisture values
Use dry-basis moisture contents and a coefficient stated per one moisture-content percentage point.
Inputs Movement coefficient · Initial wood moisture content · Final wood moisture content
Enter the species-specific fiber saturation point
Both moisture values must be below the sourced point. The calculator supplies no universal species value.
Inputs Species-specific fiber saturation point
Formula and variables
Approximate dimensional change = starting dimension × supplied fractional coefficient per MC percentage point × (final MC − initial MC).
- D₀Starting dimension
- Measured original width, thickness or length.in
- kMovement coefficient
- Sourced linear coefficient for species and grain direction.fraction per MC point
- MC₂ − MC₁Moisture change
- Final minus initial moisture content.percentage points
What the result means
Result interpretation
The tool displays the absolute estimated change and the estimated final dimension. Direction follows whether final moisture is above or below the initial value; the result does not size a structural clearance.
Limits and assumptions
Both moisture values must be below the entered species-specific fiber saturation point. Coefficient conventions vary by species, grain direction and source; no coefficient is supplied by default. This estimate does not size a structural gap or approve a fit.
Worked example
Estimate movement from 6% to 10% MC
Assumptions
- The coefficient 0.0025 is documented for the species and grain direction.
- Both moisture contents are below the entered 30% fiber saturation point.
Calculation
- 12 × 0.0025 × (10 − 6) = 0.12 in increase.
- 12 + 0.12 = 12.12 in estimated final dimension.
| Estimated dimension change | 0.12 in |
|---|---|
| Estimated final dimension | 12.12 in |
Common questions
- Can I reuse a coefficient for every wood species?
- No. Use a sourced coefficient for the specific species, grain direction and convention.
- Does the output recommend a gap or fit?
- No. It estimates movement only and is not a structural or fit recommendation.