MachineCalcs

Wood Movement / Shrinkage Calculator

Estimate across-grain wood movement from board width, starting and final moisture content, grain orientation, radial/tangential shrinkage and fiber saturation point.

Materials 9 inputs 8 results
Used in Woodworking 25

Calculator

Inputs

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Choose a screening shrinkage preset, or choose custom/measured stock to enter radial, tangential and FSP values directly.
Width measured across the grain, not along the board length. Wood movement along grain is usually much smaller.
in
Starting wood moisture content.
% MC
Expected equilibrium or service moisture content.
% MC
Flat-sawn boards move mostly tangentially. Quarter-sawn boards move mostly radially.

Results

Default result
Edit inputs
Movement magnitude(|dW|)
0.2211in
Caution

shrinkage

Also computed

Final width(W2)11.7789in

Signed width change(dW)Caution−0.2211in

shrinkage

Movement percent(|dW|/W0)1.843%

Tangential change(dW_t)−0.2211in

Radial change(dW_r)−0.1029in

MC change below FSP(dMC)−6% MC

Signed width change vs Final moisture content (%)Movement is plotted from the entered starting moisture content to possible final moisture contents below FSP. Negative values mean shrinkage.Signed width change vs Final moisture content (%)−0.500.510102030entered final MCFinal moisture content (%)Signed width change (in)
Movement is plotted from the entered starting moisture content to possible final moisture contents below FSP. Negative values mean shrinkage.
Method notes 4 notes
  • Approximation: width change = width x total shrinkage x (final MC - initial MC) / fiber saturation point.
  • Only moisture below the fiber saturation point is used. Moisture above FSP is clamped because free water has little dimensional effect.
  • Species preset: Red oak (8.6% tangential, 4% radial, 28% FSP). Presets are screening values; measured stock or a species reference is better for final clearance work.
  • Species, grain angle, juvenile wood, reaction wood, restraint, finish, temperature and actual equilibrium moisture can shift real movement.

Wood movement below the fiber saturation point can be estimated from dW = W0 x S x (MC2 - MC1) / FSP, where W0 is board width, S is total radial or tangential shrinkage, and MC is moisture content. This calculator can use common species shrinkage presets or custom measured values, then returns movement magnitude, signed width change, final width and radial/tangential comparison.

Continue workflow

All Materials
Workflow placement Woodworking Stage 3: Check behavior and finish
Next 1 Estimate lumber weight Carry actual board width and density into payload or shipping-weight estimates. Next 2 Estimate board feet Use the same actual dimensions for board-foot volume, waste allowance and lumber cost. Next 3 Build cut list Run part lengths and overage separately after moisture movement risk is understood. Chart Use reference data Material density chart

How to use this calculator

  1. Enter width across grain. Use the board or panel width in the direction that will move.
  2. Enter moisture contents. Set the starting moisture content and expected final or service moisture content.
  3. Choose species and grain orientation. Use a species shrinkage preset or custom values, then choose flat-sawn/tangential, quarter-sawn/radial, mixed or a custom coefficient.
  4. Review movement. Check movement magnitude, signed width change, final width and the moisture sensitivity chart.

How it works

Across-grain wood movement is estimated as a linear share of the total shrinkage from fiber saturation point to oven-dry: dW = W0 x S x (MC2 - MC1) / FSP A negative result means shrinkage; a positive result means swelling.

Flat-sawn boards usually move closer to the tangential coefficient. Quarter-sawn boards usually move closer to the radial coefficient. Species presets fill in those shrinkage values and FSP for screening; custom mode lets you enter measured or reference data directly. For the exact movement search path, use the wood movement calculator. For material quantity and load planning, pair this with the lumber weight calculator and board feet calculator.

Worked example

Verified against the live calculator

A 12 in flat-sawn board going from 12% MC to 6% MC, with custom 8% tangential shrinkage and 28% FSP, shrinks about 0.206 in. The final width is about 11.794 in.

Frequently asked questions

How do you calculate wood shrinkage?

Below the fiber saturation point, this calculator treats movement as proportional to moisture-content change: width change equals width times total shrinkage times the moisture change divided by FSP.

Should I use radial or tangential shrinkage?

Use tangential shrinkage for flat-sawn boards and radial shrinkage for quarter-sawn boards. Mixed grain or unknown boards are only an approximation.

Why does the calculator clamp moisture above FSP?

Dimensional movement is mainly tied to bound water below the fiber saturation point. Free water above FSP changes weight more than size.

Does this replace species data?

No. The species presets are screening values. Choose custom/measured stock when you have better radial, tangential or fiber-saturation data for the exact material.

Method & assumptions

  • Uses a linear shrinkage approximation below the fiber saturation point.
  • Movement is across grain. Longitudinal movement along the grain is not modeled.
  • Species presets are screening inputs; use measured or source-specific shrinkage data for final clearance decisions.
  • Panels, glue-ups, restraint, finish, actual equilibrium moisture, grain angle and species variation can change real movement.
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