That depends on the thickness of the finish jamb material.

If the finish trim is 3/4" thick, allow 1&1/2" for the jambs(one on each side) added to the clearance recommended by the door manufacturer.That clearance is so the door can be opened and not hit the jamb. For a 3/4" thick door, a half inch is usually enough.

That is a total of 2&1/2" which means the RO would be 32&1/2" wide. The height depends on the hardware used to secure the door and allow clearance. Often that can be up to 4" more than the height of the door.

Thanks for your reply. The opening will not have trim or jambs. It will simply be finished drywall. Perhaps the question should have been "what size should be finished opening be to hang a 30 inch wide bi-fold?".

Thanks for your help.

1" for the drywall(1/2" each side) and clearance for the door.

Probably a RO of 31&1/2" to 32".