Use this construction calculation for preliminary quantity, geometry, material, load, or coverage planning when dimensions and units have been measured consistently.

Width Millimeters (mm)

Required number input.

Movement Per Percentage Point (1/%)

Required number input.

Moisture Increase Points (%)

Required number input.

Allowance for predicted board expansion from width, a supplied across-grain movement coefficient and rise in moisture percentage points. 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]

Required Gap Millimeters (mm)

The resulting required gap millimeters returned as a number.

• Lumber calculations depend on actual dimensions, species, grade, moisture content, defects, treatment, orientation, and waste. Nominal size and average density are not substitutes for the specified product or structural grading.
• 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.

Verify dimensions on site, use current product data and local code requirements, include an explicit waste or safety allowance where appropriate, and obtain qualified structural, electrical, plumbing, or geotechnical review when required.

• Board Feet

  Calculate lumber board feet from nominal or actual thickness and width in inches and length in feet: thickness×width×length/12.

• Lumber Defect Percentage

  Rejected portion of a lumber length from total measured defect length divided by the original board length.

• Lumber Shrinkage Percentage

  Linear shrinkage percentage from the larger initial dimension and smaller final dimension measured along the same grain direction.