Woodworking & Construction Calculators

Fine woodworking & cabinetry

Wood Movement Calculator (Shrinkage and Expansion)

Change ≈ width × coefficient × ΔMC. Flatsawn uses the tangential coefficient; quartersawn uses radial. Coefficients are the USDA Forest Products Laboratory (Wood Handbook) values per 1% moisture content, measured between 6% and 14%.

Inputs

Units
in
%
%

Results

Width change
-0.175in

Negative means the board shrinks.

Final width
11.825in

The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.

Example products

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Calculation method

Across the grain, wood moves with moisture. Tangential (flatsawn) movement is larger than radial (quartersawn). Lengthwise movement is ignored here because it is tiny for furniture. Maple means hard maple, pine means southern yellow pine (eastern white pine moves less), and walnut and cherry are the black species.

Exact formula

finalWidth = width + width × coeff × (endMC − startMC). Negative change is shrinkage. Moisture above 30% (fiber saturation) counts as 30%, because wood does not swell or shrink above it.

Metric widths

A 300 mm flatsawn oak panel uses the same coefficients; only the width unit changes.

Frequently asked questions

How do I pick start and end MC?

Start is the board in the shop, measured with a meter. End is the indoor EMC at the opposite season: heated houses often drop to about 6% in winter and rise to 10–11% in a humid summer. Run both extremes to size the gap.

Why is quartersawn calmer?

Radial coefficients are smaller. That is why quartersawn panels cup and move less across their width. Riftsawn boards fall between the two values.

Should tabletops be glued tight to the apron?

No. Fasten them with buttons or figure-8 clips and leave at least the calculated change as slot travel. If the top is at mid-range moisture now, leave room to move both ways.

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