What is the fiber saturation point (FSP)?

The fiber saturation point (~28–30% MC) is the moisture content at which wood cell walls are fully saturated but no free water exists in the cell cavities. Below the FSP, wood shrinks or swells linearly with moisture change. Above the FSP, no dimensional change occurs.

Why are tangential and radial shrinkage different?

Wood is anisotropic. Tangential shrinkage (across the growth rings) is typically 1.5–2× greater than radial shrinkage (perpendicular to the rings). This difference causes flat-sawn boards to cup and warp more than quarter-sawn boards.

What does longitudinal shrinkage mean?

Longitudinal shrinkage occurs along the grain (the length of the board). It is very small — usually less than 0.1% for normal lumber — and is often ignored in practice, but it can matter for long structural members.

How accurate are these coefficients?

The coefficients are average values from USDA Forest Products Laboratory data. Actual shrinkage varies within a species based on growth rate, density, and local growing conditions. Use a 10–15% safety margin for critical applications.

Does this calculator work for green (freshly cut) lumber?

Yes. Set the initial MC to the green MC of your species (typically 80–120% for hardwoods, 30–200% for softwoods) and the target MC to 6–8% (typical indoor EMC). The formula only applies below the fiber saturation point, so values above ~28% are clamped to 28% for the calculation.

What is equilibrium moisture content (EMC)?

EMC is the moisture content wood reaches when in equilibrium with its surrounding relative humidity and temperature. Indoor conditions in temperate climates typically yield an EMC of 6–10%. Knowing the service EMC lets you predict how much installed wood will move from its installation MC.

Wood Shrinkage Calculator

Name: Wood Shrinkage Calculator
Availability: InStock
Author: Nham Vu

Calculate how much a piece of lumber will shrink or swell as its moisture content changes, using species-specific shrinkage coefficients.

Shrinkage Parameters

Wood Species

Grain Direction

Measurement Unit

Initial Moisture Content (%)

Final Moisture Content (%)

Initial Dimension (in)

Change

—

Final Dimension

—

% Change

—

of initial

Species Oak, Red

Direction Tangential

Shrinkage coefficient used 0.408 % / %MC

Effective MC change (clamped to FSP) 11 %

Formula: ΔD = D × S × ΔMC ÷ 100 • FSP clamped at 28%

0% movement

0% 5% movement

Species Shrinkage Coefficients Reference

Species	Tangential (%/%MC)	Radial (%/%MC)	Longitudinal (%/%MC)

Source: USDA Forest Products Laboratory, Wood Handbook (2010). Coefficients expressed as percent shrinkage per percent change in moisture content below FSP (~28%).

Summary

Calculate how much a piece of lumber will shrink or swell as its moisture content changes, using species-specific shrinkage coefficients.

How it works

Select the wood species from the dropdown (each species has unique shrinkage coefficients).
Choose the grain direction: tangential (flat-sawn), radial (quarter-sawn), or longitudinal (along the grain).
Enter the initial moisture content (MC) of the lumber as received.
Enter the target or final moisture content after drying or in service.
Enter the initial board dimension (width, thickness, or length) in your chosen unit.
The calculator applies the species shrinkage coefficient and displays the expected change and final dimension.

Use cases

Estimating gaps needed between hardwood flooring boards during installation.
Predicting how much a solid wood tabletop will move seasonally.
Sizing mortise-and-tenon joints to account for wood movement in furniture.
Calculating shrinkage allowance when kiln-drying green lumber.
Planning expansion gaps for solid wood paneling and wainscoting.
Comparing shrinkage behavior between species before selecting lumber.
Teaching woodworking students about moisture-related wood movement.
Verifying that door and window frame clearances are sufficient.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu