generally when measuring for any frame albeit door or window you would measure brick to brick at various points up the height and width and then deduct 10mm from the shortest measurement. this allows for the frame to be fitted true and square.
so the answer is 5mm all the way round.
but don`t forget your brickwork may not be true and level
levilewy
November 2010
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix windows and doors.