Free Door Rough Opening Calculator
Calculate the rough opening dimensions needed for a door based on the nominal door size and framing clearances.
Rough Opening Width
38.00 in
Rough Opening Width vs Door Width
How to Calculate a Door Rough Opening
Formula
RO Width = Door Width + 2 x Side Gap
RO Height = Door Height + Top Gap + Threshold Allowance
The side shim gap (typically 1 inch per side) gives room for the door jamb and shims. The top gap allows clearance for the head jamb. The threshold allowance accounts for the finished floor and threshold assembly.
Standard Sizes
Most interior doors are 80 inches tall. Common widths are 24, 28, 30, 32, and 36 inches. Exterior doors may be 36 inches wide and 80 or 96 inches tall.
Example Calculation
A standard 36-inch wide by 80-inch tall door with 1-inch side gaps, 0.5-inch top gap, and 1.5-inch threshold allowance.
- 01RO Width = 36 + 2 x 1 = 38 inches
- 02RO Height = 80 + 0.5 + 1.5 = 82 inches
- 03The framed opening should be 38 in wide by 82 in tall.
Frequently Asked Questions
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