Door Rough Opening Calculator
Calculate preliminary door rough-opening dimensions, opening area, casing length, stock trim pieces and material cost for identical doors.
Default project preview
38 × 81.5 in
Opening area
86 ft²
Casing length
143.7 ft
Trim pieces
18
Side allowance
1 in
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Rough width = door slab width + two side clearances. Rough height = door slab height + top clearance. Casing follows two sides plus the head on each selected face.
FAQ
Door Rough Opening Calculator questions
Is there one universal rough-opening allowance?+
No. Door units, jambs, thresholds and installation systems vary. Use the manufacturer rough-opening specification.
Does this calculate a structural header?+
No. Header size depends on wall type, span, loads and code.
Why is casing calculated on two faces?+
Interior doors often receive casing on both sides, but the entered face count can be changed.