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

Leaf width (mm)

Width of the door leaf in millimetres.

Gap per side (mm)

Clearance gap per side in millimetres, between zero and ten; three is typical.

Compute door frame inner width and total side gap from the leaf width and per-side clearance. 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]

Frame inner width (mm)

Required frame inner width in millimetres: leaf width plus both gaps.

Total side gap (mm)

Combined gap of both sides in millimetres.

• 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.

• Cabinet Door Gap

  Calculate the center gap of a pair of inset cabinet doors after subtracting door widths and equal side gaps from the opening.

• Tuer Luft Spalt

  Equal left and right side clearance of a centered door leaf inside a wider clear opening.

• Frame Rough Opening Calculator

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