How to Add Shims to Install a New Door

Measure up from the bottom of the doorjamb around the prehung door to the middle of each of the hinges. Transfer this mark onto the trimmer piece, which is the wood piece that is already framing the rough opening. Take into consideration the height of the bottom of the doorjamb that you will install with the pre-hung door when marking the location of the hinges.

Tack 1/8-inch thick shims at each of the hinge locations on the hinge side of the trimmer. Cut the edges of the shims off evenly so they don't stick out beyond the door frame.

Place the prehung door in the opening with the hinge side moved tightly against the shims you installed. Pound one nail through the hinge side of the frame so it is about 3 inches down from the top corner. Adjust the door as necessary to make it plumb.

Add more shims at the hinges as necessary to make the door plumb with the wall. The frame should touch the shims at all three hinge locations. Pound a nail through the door frame and shims so it goes into the trimmer piece.

Slide shims on the latch side of the door toward the top of the door so that the jamb touches the shim but isn't pushed by it. Nail through the jamb and shims into the trimmer. Add shims and nail the jamb in place the same way near the bottom of the frame, above the strike plate and below the strike plate to keep the jamb steady.

Trim any edges of the shims that stick out beyond the door frame using a utility knife.