How to Level and Square a Door Frame. If you're hanging a door, one of the most important things to do is to make sure the door frame is level and square. If not, the door won't open and close properly. Once the rough opening is finished and ready to accept the door frame, it's crucial to check and re-check that the door frame is level and square.
Things You'll Need
Wooden shims, wedges or blocks of wood
Make sure the rough opening is square by placing a carpenter's square in each upper corner of the opening. It's difficult to level and square the door frame if the rough opening isn't constructed properly.
Check that the floor is level. If you're working with an uneven surface, this affects your ability to level and square the door frame.
Place the door frame into the rough opening. Use wedges or shims on the door hinge side for proper centering of the door frame in the opening. Nail them into place near each hinge.
Ensure that the door sill is level. Use a flat bar or wedge under the latch side of the door frame to raise it as far as necessary. Have someone hold it in place and check the top, or lintel, of the door frame to make sure it's level.
Insert wedges or shims on the latch side of the door frame and nail the frame into place. Make sure that the gap between the door frame and rough opening is the same around the entire frame.
Slip blocks of wood or shims over the lintel to attach the top of the door frame to the rough opening. Check each corner with a square before nailing top of frame into place.
Check level and square of door frame throughout this process. Don't hammer nails all the way in case you have to remove them in order to reset the door frame. Always nail hinge side of door frame into place first.