Why does wood shrink and expand?

Wood is hygroscopic — it absorbs and releases moisture from the air. As moisture content decreases below the fibre saturation point (around 28%), the wood cells shrink. Wood moves most across the grain (tangentially) and least along the grain (which is negligible).

What is the fibre saturation point?

The fibre saturation point (FSP) is the moisture content at which the cell walls are fully saturated but there is no free water in the cell cavities — typically around 27–30%. Below this point, further drying causes the wood to shrink. Above it, additional moisture causes no dimensional change.

What moisture content should I target for furniture?

In the UK, indoor furniture should be at 8–10% moisture content. For centrally heated rooms, aim for 8%. For less-heated spaces, 10–12% is appropriate. Outdoor furniture should be around 14–18% MC.

Does quarter-sawn wood move less?

Yes, significantly less. Quarter-sawn boards shrink and expand radially (across the rings), which is typically about half the tangential movement of flat-sawn boards. This is why quarter-sawn timber is preferred for tabletops, drawer sides, and panel construction.

How do I measure wood moisture content?

Use a pin-type or pinless moisture meter. Pin meters are more accurate for specific depths; pinless meters scan larger areas. For woodworking, a meter accurate to ±1% MC is sufficient. Always take readings from the middle of the board, not the ends.

WoodCalcs

Wood Shrinkage Calculator — Dimensional Movement

Estimate wood movement due to moisture content changes. Plan expansion gaps and allowances for seasonal movement.

Wood Species

Grain Orientation

Board Width (across grain)

Width measured across the grain direction

Current Moisture Content

MC of timber now

Target Moisture Content

Expected MC in final location

How We Calculate This

This calculator estimates dimensional change in wood due to moisture content (MC) changes, using species-specific shrinkage coefficients.

The formula

Shrinkage (%) = MC change × Shrinkage coefficient

Dimension change (mm) = Board width × Shrinkage (%)

Shrinkage coefficients

Each wood species has two coefficients: tangential (across the growth rings, flat-sawn) and radial (through the rings, quarter-sawn). Tangential movement is always greater than radial — typically by a ratio of about 2:1.

Important notes

Shrinkage only occurs below the fibre saturation point (~28% MC)
Movement along the grain is negligible (0.1–0.2%) and is not calculated
Actual movement can vary by ±20% from calculated values

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.