Door Frame Size Calculator
Calculate door frame dimensions including jamb, header, and rough opening sizes. Enter values for instant results with step-by-step formulas.
Reviewed by Abdullah, Technical Content Specialist
Formula
Rough Opening Width = Door Width + 2.0 in; Rough Opening Height = Door Height + 2.5 in
The rough opening must be larger than the door to accommodate the jamb material, shimming space for leveling, and bottom clearance. Jamb width must match the total wall thickness including drywall or sheathing on both sides.
Worked Examples
Example 1: Standard Interior Bedroom Door
Problem:Calculate the rough opening and material needs for a 30 x 80 inch interior door in a standard 2x4 wall with drywall.
Solution:Rough opening width = 30 + 2.0 = 32.0 inches\nRough opening height = 80 + 2.5 = 82.5 inches\nJamb width = 3.5 (stud) + 0.5 + 0.5 (drywall) = 4.5 inches\nTotal jamb = 2 x 82.5 + 32.0 = 197.0 inches = 16.4 linear feet\nCasing = 2 sides x (2 x 82.5 + 35) = 400 inches = 33.3 linear feet
Result:Rough Opening: 32 x 82.5 inches | Jamb: 16.4 ft | Casing: 33.3 ft
Example 2: Wide Exterior Entry Door
Problem:A 36 x 80 inch exterior door in a 2x6 wall. What are the frame dimensions and header requirements?
Solution:Rough opening width = 36 + 2.0 = 38.0 inches\nRough opening height = 80 + 2.5 = 82.5 inches\nJamb width = 5.5 + 0.5 + 0.75 (sheathing) = 6.75 inches\nHeader size: 38 inches wide = double 2x6 (load-bearing)\nShim pairs = ceil(80/16) x 2 + ceil(36/16) = 10 + 3 = 13
Result:Rough Opening: 38 x 82.5 inches | Header: double 2x6 | 13 shim pairs needed
Frequently Asked Questions
What is the standard rough opening size for an interior door?
The standard rough opening for an interior door is 2 inches wider and 2.5 inches taller than the door slab itself. For the most common 36 by 80 inch door, the rough opening should be 38 by 82.5 inches. This extra space accommodates the door jamb material, shimming gaps for plumb and level adjustments, and clearance at the bottom for flooring. The 2-inch width allowance breaks down as roughly three-quarters inch jamb material and one-quarter inch shim space on each side. Always verify your specific door manufacturer recommended rough opening dimensions.
What are the standard interior door sizes?
Standard interior door widths include 24 inches for closets, 28 inches for bathrooms, 30 inches for bedrooms, 32 inches for larger bedrooms, and 36 inches for main entries and accessibility compliance. The standard height is 80 inches (6 feet 8 inches) for most residential applications. Some custom and modern homes use 84-inch or 96-inch tall doors for a more dramatic appearance. The standard thickness is 1 and three-eighths inches for interior hollow-core or solid-core doors. Exterior doors are typically 1 and three-quarters inches thick for greater security and insulation.
How much casing trim do I need for a door frame?
Each side of the door requires two vertical pieces and one horizontal piece of casing trim. For a standard 36 by 80 inch door, each vertical piece is approximately 82.5 inches and the horizontal piece is about 41 inches. With two sides of the wall, you need four vertical pieces and two horizontal pieces totaling approximately 412 inches or about 34.3 linear feet. Always add 10 to 15 percent extra for miter cuts and waste. If using mitered corners, each piece needs an additional 3 to 4 inches beyond the visible length to account for the 45-degree angle cuts.
Where should door hinges be placed on the frame?
Standard hinge placement for a three-hinge door positions the top hinge 7 inches from the top of the door, the bottom hinge 11 inches from the bottom, and the middle hinge centered between the two. For taller doors of 84 inches or more, four hinges are recommended with equal spacing between them. Hinge mortises should be cut with a router and hinge template for precise, consistent depth. The mortise depth should match the hinge leaf thickness so the hinge sits flush with the jamb surface. Exterior and heavy solid-core doors should always use three or more hinges to prevent sagging.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy