Rookie door hanger here. I'm trying to hang a prehung door in my opening. It's a standard 2x4 framing, the door is a standard 2x4 prehung door here: https://www.lowes.com/pd/Masonite-Classics-6-panel-Single-Prehung-Interior-Door-Common-30-in-x-80-in-Actual-31-5-in-x-81-5-in/1000061087

I've got everything up for the one side and just went to put the other side up and the pieces do not meet. The framing is about 1/4 too wide for the door jamb? I'm not sure what I did wrong. The framing is 2x4's and the drywall that goes up to the edge like it should is 5/8 inch. What did I do wrong?

  • If you haven't already finished installing this door - stop and take a very close look at the door jamb. I installed one of these a few days ago, and discovered that the jamb is adjustable!. All around it's made up of 2 pieces with a sort-of tongue-and-groove arrangement which lets you size the door jamb to your wall.
    – brhans
    Oct 1, 2017 at 0:42

3 Answers 3


The standard jamb is 4.5 inches and is based on an assumption of .5 drywall on each side (.5 dw + 3.5 stud + .5 dw).

When a different thickness of finish material is being used, custom jambs can be ordered or constructed onsite. If you use standard prehungs with conventional widths, you need to create a jamb extender.

The simplest way is to install the jamb flush with the finish material on one side and attach the extender to the other side. You can use a trim strip, such as a flat lattice piece or other thin material around .25 inch thick. It can be glued and tacked to the edge of the jamb.

While you could try to get the extender exactly flush with the edge of the existing jamb, such joints are rarely exact and tend to leave a seam, even if filled. Most finish carpenters do not try to do exact aligns, but use a reveal, a slight offset that looks intended. In this case, move the extender trim about .125 (1/8th inch) away from the door opening, toward the drywall. Glue and tack. Once painted it will add a detail that enhances rahter than looking like a fix of a mistake.

  • Thank you, this is the way forward I guess. I started it and it seems to be how it has to go.
    – cclater
    Sep 30, 2017 at 23:08

A bare 2x4 wall without Sheetrock is 3 1/2" wide and with 1/2 Sheetrock on both sides it is 4 1/2" wide. A pre-hung door for a 2x4 wall will have a 4 1/2" wide jamb so that it sits flush with the Sheetrock on both sides and then the trim goes over the small gap between the door jamb and Sheetrock. Meaning that when the door is installed the jam is proud of the stud by half and inch so that the Sheetrock will but up to the jamb. If you have 5/8 rock on both sides then then you have a 1/4" difference.

You will need to fill that gap, i would rip pine board to a 1/4" inch and fill the gap, fill the seam with wood filler and sand it and paint it. Or you could fill it with backer rod and caulk it or fill with some other filler but it does not look as good in my opinion. Or you could build a jamb to fit the space you have.


I have installed 10 pre-hung doors and finally got it right by barely acceptable DIY standard on the last few. All mine were with 1/2" drywall on both faces.

If you have lined up the jamb on one face of drywall and if have 5/8" drywall on both sides, that would account for 1/4" short on the other face.

Have you nailed it on either side? If not you might be able to center the door jamb in-and-out to leave only 1/8" on each drywall face and then used special trimming to fill in the 1/8" gap on each face.

Or maybe leave it flush with one face and fill in 1/4" on the other face. Finish carpenters here will probably be able to tell you just how to do it. Do you have access to a table saw as well as a miter saw?

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