Wood Moisture Content and Movement

Wood is ready to cut after 1-2 weeks in the shop, when its moisture sits within 2 percentage points of the room.

Kiln-dried furniture lumber is sold at 6-8% moisture content. That figure is a starting point, not a permanent property: wood exchanges moisture with the air around it, so a board stored somewhere damp arrives at the bench wetter than the tag claims.

The acclimation procedure is patience with a number attached. Let the boards sit in the shop for 1-2 weeks, and cut only when the board's moisture is within 2 percentage points of the room's equilibrium moisture content. The room where the shelf will live is the target, not the room where the saw happens to be.

The reason is movement, and it has a formula. Wood moves across the grain by roughly 1 mm per 100 mm of width per 4% change in moisture content. A 300 mm wide panel can therefore change width by about 6 mm between 6% and 14% moisture — more than enough to open a glue line or bow a shelf side.

Movement along the grain is a different story: under 1 mm per metre. That is why a 900 mm shelf can be cut to a tight length without worry, while its 300 mm depth is the dimension that swells and shrinks through the seasons.

Design with the grain direction in mind and the numbers stop being a threat. Leave the width free to move, keep the length exact, and glue up only after the 1-2 week wait. The seven-step build on the main page starts at exactly this step, and the sizes page explains which boards and sheets you will be waiting on.

• Boards have sat in the shop for 1-2 weeks.
• Measured moisture is within 2 percentage points of the room.
• Kiln-dried stock started at 6-8% — confirm it stayed near that.
• Wide panels around 300 mm are treated as parts that can swing about 6 mm.
• Length cuts are safe: along-grain movement stays under 1 mm per metre.

Further reading

• Nominal vs Actual Lumber Sizes
• The First Tools for a Small Woodshop