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

Door assembly width (mm)

Complete pre-hung door assembly width in millimeters.

Door assembly height (mm)

Complete pre-hung door assembly height in millimeters.

Compute the masonry rough opening from the door assembly size using total allowances of plus 10 mm width and plus 5 mm height. 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]

Rough opening width (mm)

Required rough opening width in millimeters including the 10 mm allowance.

Rough opening height (mm)

Required rough opening height in millimeters including the 5 mm allowance.

• 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.

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