Project tools

Wood Movement Planner

Calculate how much a board will expand or contract as moisture content changes. Includes tangential vs radial orientation.

Related guides Species data

You do not need to be an engineer. Change any box below—the big number updates straight away. If "moisture %" is new to you, skim Quick start first.

Quick start

Pick your wood type. The tool estimates movement for its width—if typical fallback data is used, a yellow note will appear.
Slide board width to the measurement across the plank you're worried about (say a wide table top), not the long length running along the grain.
Moisture when fitted is roughly how damp it was when you built it. Moisture indoors later is after the heating's kicked in—guess if needed; a sensible gap is the goal, not a lab test.
Choose flat-sawn vs quarter-sawn: flat-cut usually swells and shrinks more across the grain than quarter-cut at the same width.

What each thing means

Timber species: Sets how "active" the tool uses for this species on average. Link "Species data" above if you want background on the timber itself.
Board width (slider): The width across the grain in millimetres—the direction that grows and shrinks with damp and dryness. Wider pieces move more millimetres in total.
MC installed / MC in service: Moisture as a percentage is what handheld meters show in DIY use. Put one reading for fitting day and one for drier indoors life later. Farther apart means expect more shrink or swell.
Flat-sawn vs quarter-sawn: How the log was sliced changes how much face swells sideways. Wrong choice here makes the estimate too big or too small.

No saved movement data found for this species — typical values for this wood type have been used instead. Totals are ballpark-safe.

Inputs

Enter real measurements or rough guesses—both beat leaving defaults if you forgot to measure.

Timber speciesBoard width (150mm)

MC installed (%)MC in service (%)

Results

Estimated movement

4.2 mm

2.8% of board width

MC change

10%

Sensitivity

0.0028 / % moisture

Recommended gap

3mm

Orientation

Tangential

Timber gets wider when it's damp and narrower when it dries. We mix a typical "wiggle factor" for your wood, how far apart your two moisture numbers are, and the width you slid—other online tools add extra steps and may land near this but not on the nose. Heating, paint, and screwing it tight across the grain all still change what you see on site.

Quick start

Pick your wood type. The tool estimates movement for its width—if typical fallback data is used, a yellow note will appear.
Slide board width to the measurement across the plank you're worried about (say a wide table top), not the long length running along the grain.
Moisture when fitted is roughly how damp it was when you built it. Moisture indoors later is after the heating's kicked in—guess if needed; a sensible gap is the goal, not a lab test.
Choose flat-sawn vs quarter-sawn: flat-cut usually swells and shrinks more across the grain than quarter-cut at the same width.

What each thing means

Timber species: Sets how "active" the tool uses for this species on average. Link "Species data" above if you want background on the timber itself.
Board width (slider): The width across the grain in millimetres—the direction that grows and shrinks with damp and dryness. Wider pieces move more millimetres in total.
MC installed / MC in service: Moisture as a percentage is what handheld meters show in DIY use. Put one reading for fitting day and one for drier indoors life later. Farther apart means expect more shrink or swell.
Flat-sawn vs quarter-sawn: How the log was sliced changes how much face swells sideways. Wrong choice here makes the estimate too big or too small.

Get better results

No meter yet? Indoor "dry-ish" timber is often around 9–11 %; greener workshop stock might land in the teens or higher—you can still punch numbers to see bracket sizes.
Big glued-up panels mostly move like flat-cut stock across the glued width—don't assume magically stable widths without detail.
Wide tops still creep seasonally: screws through slightly elongated holes or tabletop buttons beat gluing rigidly across the grain into a cage.
Paint/varnish slows swings but rarely stops them—still leave room for shrink/swell.
If you're not sure oak = oak naming in the dropdown, glance Species data.

Reading the numbers

The headline millimetres is how much narrower or wider expected across the face you typed—not along the plank length. The percent line is that motion as a slice of board width. Sensitivity is a nerd number baked into those sums—you can mostly ignore it if you're just checking gaps.

Not a substitute for structural sign-off

Weekend maths only—glue, heating, coats across the grain, Building Regs, and real messy trees argue back. Anything structural or regulated needs whoever legally signs drawings where you live, not this web page.