How much space should be allowed between studs to allow for a door?
For example, if the finished door has a 30" opening, then what should be the distance between the framing studs that enclose the door?
Normally rough opening is 2 inches larger then the nominal door size. This leaves approximately 1/4" on each side for shimming to plumb.
Some carpenters prefer 2-1/2", leaving a 1/2" gap for shimming. In case framing isn't very precise (say when using unskilled volunteer labor), 1/4" can sometimes be inadequate.