2 inches wider than the door itself.
You are supposed to measure the "rough" opening. This is distance from the studs that line the door opening. (not from the door frame itself) Top to bottom then from side to side. If you already have a door there and are just replacing it then you can just measure the door and get one of the same size. Good luck.
The rough opening of an interior door is two inches wider than the width of the door and two inches higher than its height. Thus your rough opening width is 38". A typical interior door has a height of 80" which would require a rough opening height of 82" but check your door to ensure that is theheight.
The margin is the space between a door and its frame. The frame should always be slightly larger than the door to allow for easy opening and closing.
A door frame is the rough opening that the door and door jam go in to. Door frames are part of the framing of a house and the door jam is the out side frame that the door sits in.
A 3680 door is 3'-6" wide. After hanging on a frame the clear opening will be smaller by the thickness of the door stop, so the net opening of the door frame will be about 3'-5" wide.
The rough opening width for a 24" door is 26-1/2" The rough opening height for a 24" door is 26-5/8" Rough openings are 2" wider and 2-1/2" taller than the actual door. This allows room for the door frame and adjustment.
Remember 36" is the width of you door slab. If you can measure the door you want to frame in then take the measurement and add 3/4" to it so you can still have room on the side to shim it properly. If you don't have the door but know which one you want, go to the store and the door will normally have the rough opening size on the label.
The rough opening for any door or window less than 82.5 inches is two inches larger than the frame being placed in. If the door is larger than that, two and one half inches are added to the overall size.
The finished wall width after wall coverings are applied.
Width (excluding door mirrors): 66.1 in. (1.68m) Width (including door mirrors): 76.4in. (1.94m).
A residential main entry is 3 ft - 0 inches wide and 6 ft 8 in tall. The rough opening for the door and frame to fit into is 3 inches larger on the width and 1-1/2 inch on the height which will allow for the door and jamb and also any necessary adjustment required to plumb and/or square the door unit.
There is no standard door width as they come in 2" increments up to 36" wide. A common door jamb width is 4-9/16" width, this is for a 2x4 wall and 1/2" drywall on both sides.