Interior door sizes have evolved as the homes got bigger and taller. While in 1980 the median size of a new home in the U.S. was 1,595 square feet, in Q4 of 2021 the median size of a new single-family home increased to 2338 square feet, as reported by the Census Quarterly Starts and Completions by Purpose and Design. With this increase in the floor area, the architectural design pushed the typical room height over the same period from 8' in 1980' to 9' in 2020' (finished floor to finished ceiling).
Standard door height in 2023 — For new residential home construction starting in 2023 expect to see 8' tall doors in 9' tall ceilings as standard. In high-end homes you may see 9' tall full-height doors (floor-to-ceiling doors) for the same 9' ceiling height.
Standard door width in 2023 — Standard (and most common) interior door widths in American homes are 30, 32, 34, and 36". These width dimensions have not changed as much the height.
American interior doors are usually available in increments of 2", giving you a range of typical door widths of 28", 30", 32", 34", 36".
In Europe, the door sizes are typically given in millimeters, for example, 800 x 2100 mm. Some European countries have their customary dimensions — for example, standard door widths in Germany, Austria, and Switzerland are 610, 735, 860, and 985 mm. These dimensions come from the German Institute for Standardization called DIN (Deutsche Institut für Normung). Meanwhile, the standard door widths in Italy or the Czech Republic are 600, 700, and 800 mm.
When it comes to the door proportion (height-to-width), you'll find the ideal balance in 3-to-1 door-heigh-to-door-width ratio, so 32"x96" (architectural call size 2880) is perfect.
The door marks used by architects and builders (GC) in their floor plans, door schedules and construction documents may look confusing for the untrained eye.
Let's say you see this  door mark next to a door symbol in the floor plan. The door mark represents a door size, not a door number. Door marks are frequently just four digits long but can have 5 or 6 digits. To decipher the number, parse the door mark into feet and inches. In our example, 2880 should really be written as 2'8" x 8'0", meaning our 2880 door will have the size of 32" x 96" in inches (not 28"x80" as it may appear).
This door mark (such as 2880) is sometimes called call size or architect call size in construction documents and door manufacturer's technical documentation.
A rough opening is the space cut out of a wall where a window or a door will get mounted. Technically, the rough opening is the structural frame that surrounds the door unit. The dimensions for the rough opening are from jack stud to jack stud (vertical studs) and from header to floor.
Is there a difference between a rough opening (R.O.) and finished opening (door size)? Yes, the "rough opening" is the size of the opening in the wall before a door is hung/installed, while the "finish opening" is the final size of the opening with the door installed - which translates to net clear opening width and net clear height.
As a rule of thumb, customary interior doors require 2" (51 mm) for width and 2 ½" (64 mm) for height — however, each door manufacturer has their own R.O. requirements for every model they make (i.e. fire-rated doors may have much larger R.O. requirements).
Frameless doors, sometimes called invisible or hidden doors, typically have a different R.O. requirement because the door frame (jamb) is recessed in the wall assembly. Using the same example of a 2880 door (32"x96"), the Dorsis Fortius invisible door would require a rough opening of 36 ½" x 98 ¼".
In the United States, the state and local building codes have additional minimum door width requirements specifically for commercial buildings — they require the minimum door width for wheelchair access as 32" (see ADA Standards for Accessible Design). It is critical to know that the 32" wheelchair minimum references the clear passage (net width), meaning it is the narrowest dimension when the door is open.