Door size compared to frame size

[Possom]

2. Measure the height, width, and depth of the door opening. he new door should be ½” less than the height of the rough opening and ¾” less in width.

http://www.lowes.com/cd_Install+an+Exterior+Door_554148183_

Would you not require a door to be less than the door opening in height and width by perhaps only 1 or 2mm?

Less by 1/2" in height and 3/4" to me would seem like a very large gap between the door and the frame.

 

[ronniecabers]

As you say , they are big tolerances! Our guys tend to try and get either the inside face , or outside face , behind the reveal ( if poss both ) Can be a little tricky to fit sometimes but just looks better and is a more secure fit . I am surprised at those tolerances. I do notice its an American site so maybe thats how they fit their doors.....

 

[ree]

They are referring to the "rough opening" which in stud framing means the dimension between trimmer studs (AKA jack studs) on either side of the rough opening. In UK terms it would mean the width between the brick reveals of an opening.

In the UK my suggestion is you should leave 2mm to 3mm all around but it depends on if the door is to be painted etc.