Does wood shrink when moisture content falls?

Wood can change dimension as moisture content changes, with movement depending on species, grain direction, moisture range and conditioning history.

What does the shrinkage coefficient mean?

In this calculator, the coefficient is the percentage of dimensional change associated with a one-percentage-point moisture change over the range being estimated.

Is wood shrinkage the same in every direction?

No. Wood anisotropy means tangential and radial movement can differ substantially, while longitudinal movement is usually much smaller.

Can this predict exact final lumber size?

No. It is an estimate based on user-supplied assumptions and does not model species-specific sorption behavior, grain orientation or manufacturing tolerances.

Can I use a supplier-specific shrinkage value?

Yes. A documented coefficient for the relevant species, direction and moisture range is preferable to a generic assumption.

Timber movement estimator

Wood Shrinkage Calculator: Moisture Change & Final Size

Estimate how a timber dimension may change when its moisture content moves from an initial value to a final value. Enter the shrinkage coefficient that matches your material and direction, then see both the dimensional movement and estimated final size.

Moisture and dimension inputs

Initial dimension

Dimension unit

Initial moisture content (%)

Final moisture content (%)

Shrinkage coefficient (% per 1% MC)

Movement direction

Use a coefficient appropriate to the species, grain direction and moisture range. The calculator intentionally does not invent a universal wood-species coefficient.

Enter the initial dimension, moisture values and coefficient.

Estimated dimensional change

—

—Dimensional movement

—Estimated change

—Moisture change

—Direction

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How the wood shrinkage estimate works

This model treats the supplied coefficient as a linear screening factor. The moisture-content change is multiplied by that coefficient to estimate the percentage dimensional movement.

Moisture change = initial MC − final MC
Estimated dimensional change (%) = moisture change × coefficient
Final dimension = initial dimension × (1 − dimensional change ÷ 100)

Why grain direction matters

Wood is anisotropic, so movement is not identical in every direction. Tangential and radial dimensional movement can differ substantially, while longitudinal change is usually much smaller. A coefficient should therefore be selected with the actual grain orientation in mind.

Example

Suppose a 150 mm dimension moves from 20% moisture content to 12%, and the assumed coefficient is 0.25% per percentage point. The estimated dimensional change is 8 × 0.25 = 2%. A linear screening result would therefore be 150 × 0.98 = 147 mm.

Why this is only an estimate

Real timber movement depends on species, density, growth characteristics, grain orientation, conditioning history, relative humidity and whether the moisture change occurs above or below the fibre saturation region. Machining tolerances and restraint can also change the observed result.

For design-critical or precision woodworking applications, use species-specific technical data and the moisture range appropriate to the product rather than treating this coefficient as a universal law.

Interpreting the result

A small percentage change can become significant across wide boards, panels and fitted components. A calculated movement of 2% across a 600 mm component represents about 12 mm, which is very different from 2% across a 50 mm trim piece.

Frequently Asked Questions

Does lower moisture always mean the same amount of shrinkage?

No. The relationship can be species- and moisture-range-dependent. This tool uses the user-supplied simplified coefficient.

Which direction usually moves more?

Tangential and radial movement are generally much more important than longitudinal movement, but the actual values depend on the wood and moisture range.

Can I use a supplier's coefficient?

Yes, and that is preferable when the coefficient is documented for the relevant product.

Does this calculate timber weight loss?

No. It estimates dimensional movement only.

Does restraint matter?

Yes. Fasteners, joints, laminations and other restraints can alter how movement appears in an assembly.