Door Size FAQ
Find answers to common questions about standard U.S. door sizes, door widths and heights, rough openings, prehung doors, and metric conversions.
Common Door Size Questions
What is the most common interior door size?
Common interior door sizes include 24, 28, 30, 32, and 36 inches in width, with 80 inches being a common nominal height.
What is the standard door height?
An 80-inch nominal height is common for many residential doors. Taller doors, such as 84-inch and 96-inch doors, are also available.
What is a standard 30 × 80 door?
A 30 × 80 door has a nominal width of 30 inches and a nominal height of 80 inches. The actual physical dimensions may be slightly smaller.
What is a standard 36 × 80 door?
A 36 × 80 door is a common nominal door size with a 36-inch width and 80-inch height.
What is the rough opening for a 30 × 80 door?
A commonly used planning reference is approximately 32 × 82 inches. The exact rough opening should be confirmed with the door manufacturer.
What is the rough opening for a 36 × 80 door?
A commonly used planning reference is approximately 38 × 82 inches. Actual requirements vary by door and frame system.
Door Measurement Questions
What is the difference between door size and rough opening?
Door size identifies the door itself, while the rough opening is the framed opening prepared to install the door and frame.
What does nominal door size mean?
Nominal door size is the commonly used size designation, such as 30 × 80. It does not necessarily represent the exact physical dimensions of the door slab.
How do I convert door sizes from inches to millimeters?
Multiply the measurement in inches by 25.4 to convert it to millimeters. For example, 36 inches equals approximately 914 mm.
Are all doors with the same nominal size exactly the same?
No. Actual dimensions can vary between manufacturers and product types. Always check the product specifications before ordering or installing a door.
How do I measure an existing door?
Measure the door width, height, and thickness. For replacement work, it is also useful to measure the frame and rough opening where accessible.
Prehung Door Questions
What is a prehung door?
A prehung door is supplied with the door slab already mounted in a frame, usually with hinges installed.
Is a prehung door the same size as the door slab?
No. A prehung unit includes the frame and therefore has larger overall dimensions than the door slab itself.
Should I use the door size or unit size when framing?
For new construction, the required rough opening should be based on the specific door unit manufacturer's installation instructions rather than only the nominal door size.