Rough Opening Width
The RO width is the measurement of the opening from the left stud to right stud. When determining the RO Width, you will need to add 3/4″ to the UD Width.
Rough Opening Height
The RO height is the measurement of the opening from header stud to subfloor. When determining the RO Height, you will need to add 1/2″ to the UD Height.
The unit sits in the Rough Opening. Therefore the Unit Dimension and the Rough Opening are related. If you are able to determine one, you are able to determine the other.