Use this workshop calculation to turn measured dimensions and the selected construction convention into a cut, spacing, fit, or material-planning value.

Installed clear gap (mm)

Required number input.

Expected board width change (mm)

Required number input.

Predict clear decking gap after a specified signed change in board width; positive board expansion reduces the gap. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Predicted clear gap (mm)

The resulting predicted clear gap returned as a number.

• Nominal dimensions, kerf, moisture movement, hardware clearances, wall squareness, and manufacturer instructions can change the required shop dimension. Measure the actual assembly and test critical joints on scrap before cutting finished material.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Complement the calculated dimension with a physical story stick, dry fit, or full-size layout. Follow the hardware, coating, adhesive, or machine manufacturer's limits where they differ from a rule of thumb.

• Board Expansion Gap

  Minimum total free space for expected across-grain board expansion from a supplied movement coefficient and moisture-content change.

• Trellis Lath Spacing

  Equal clear gap including both end gaps when equal-width trellis laths fill a known inside span.

• 4-Inch Baluster Spacing

  Count equal-width balusters and calculate equal clear gaps, including both end gaps, so none exceeds a four-inch maximum.