Trimming down a door frame

So I got a great deal on an unfinished door, pre-hung, the only problem is the casing is 1/4” too wide. I need to trim that 1/4”, and I’m not sure what is the best way

I’d prefer not to take the pieces of the casing apart, as they are held together with staples and dislodging them could lead to the (soft pine) boards splitting.

OTOH, I’m not sure I can make a perfectly straight cut with my hand power saw as the door sits on its side on the floor.

I’ve thought about using a trim router, but what would I run the bearing against?

I don’t know why this is being so difficult for me, but any pointers or tips to clear up my confusion would be appreciated.

(PS: The door and frame are already stained, not that it can’t be touched up if necessary. Originally I thought I would center the door with 1/8 inch “proud” on each side, and make it up with an undercut of the trim either with a dado or on the router table, but now realize that the door sits flush on one side, meaning I have to trim 1/4 from the frame itself. That’s my hang up.)

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Can you trim (widen) the “hole” instead of the pre-hung door frame? Make the space it is inserted into a little wider, and since there is usually molding (or some other finish) covering that part, it doesn’t matter much how clean it is. And even if it ends up a bit too wide, you’re going to put shims in anyway between the pre-hung door frame and the wall frame. If it’s all concrete block, then you have a bigger problem (but even concrete a can be ground down a bit if necessary, very messy though).

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Try clamping a straight edge (straight 2x4 or ?) and use that as a guide/fence to run your hand power saw along. May take rigging something up but you can get a nice straight cut .

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Goofy I am a bit confused – Can you post a labeled image showing the part/item that are bothered by?

When I was not sure about the part of a door that is the casing, Google showed me images where the “Casing” in the piece of trim that covers the gap between the door jams and wallboard on the vertical sides of the door.

It strikes me that you could pull the staples from one of the vertical casing pieces and the horizontal piece. Next shorten the horizontal piece by cutting it.

I agree with Mark, widen the opening. You really do not want to mess with the door because you could end up with a door that doesn’t close or open properly. Taking a hammer to a 2X4 on each side of the door can get a 1/4 inch out of it.


Just to clarify, I believe the OP’s problem is not the width of the door frame but rather the depth. As in the door frame is deeper then the thickness of the wall it is being installed in, thus it sticks out proud of the wall by 1/8" each side.


Thanks Sam I didn’t realize that. Well that is much easier to fix. Put the door in and just make the trim stick out further by shimming it or if you have a router table just trim the edge of the trim a little to go over the frame. Make the door in the frame fit out an 1/8th on each side.


Ah, now I understand much better. And now I know what a “proud” is.

I don’t recommend cutting it. And in general any messing with a pre-hung door renders it not pre-hung anymore.

There are 2 solutions:

  1. Install it. With 1/4" sticking out on one side. Then use your handy dandy router on a piece of molding to rout out a 1/4" indentation where necessary. This will obviously only work for moldings that are thicker than say 1/2" at that end. Install molding and hide imperfections with joint compound.
  2. Install it. With 1/4" sticking out on one side. Then get to work with your planer and/or sander to cut the 1/4" down as much as possible. Then install molding and hide the imperfections with joint compound.

Yes, I’m sorry I wasn’t clear.

The dimension between the two painted surfaces of the walls on either side of the door is 4 1/2”. (3 1/2” nominal 2x4, plus 1/2” wallboard on each side.). The pre-hung casement is 4 3/4” width (marked on the casement) so it is 1/4” too wide. [The door had a minor defect, which is probably why it was originally rejected? I repaired that with ease. But now the casement is 1/4” wider than the width it wants to occupy. The odd width is also probably why it ended up being such a deal?]

As I said, I had planned to simply undercut the trim work on each side by 1/8” and lap it over. But now that won’t work, and since the trim is only 3/8” thick I don’t think I can undercut 1/4” on one side and get away with it.,

Hope that helps.

OK – first off - I am going to assume you can put the entire ¼" on one side. Next I suggest you get some trim stock that is ¼" inch, cut a strip and slide it between the door casing and the wall. If you paint it the color of the wall, nobody who walks into your house is going to notice it – even if the casing is a stained & varnished wood.


Trim can be replaced by whatever thickness you need to allow it to be rabbited the 1/4" you need…

Maybe that frame was originally meant for a home where they’d used 5/8" drywall on both sides…


Yes, I’m sure that’s true. But since I don’t want to rip out the drywall on both sides (or even one side) I need to trim down the frame.

Several good suggestions in the thread, and I thank you for that. I’m going to go with Mark’s just to plane it down. I don’t know why I didn’t think of that, I got hung up on trying to cut it with my circular saw and knew I’d make a hash of it. I have a power planer, so it should be a simple matter to lay the whole thing on the floor, mark it and plane it down to the mark, maybe using a sander if I bump up here or there.

Thanks everyone. Things usually go smoothly, but once in a while I get hung up, and a good shove from others helps!


Not suggesting you do this, but in case you don’t know, for purposes of cosmetic cleanups, there is ¼ inch drywall. We have it at our local Home Depot.

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If the frame is made for a 4-3/4" wall and you have a 4-1/2" wall and the fame and moldings are prefinished you could take it all apart, rip the frame on a table saw, sand the edge, ease the now sharp edge with a router, touch up the edge with stain. If the opening needs adjusting you can smack it to move a little and then trim the drywall or pull one trimmer (2x4 under the head) and replace it with a 1x4 (still up to code) and trim the drywall. If the casing is too wide then it can be ripped on the thick side (not the side towards the door) all pieces need to be the same width , head and sides, or the miters will be off. -OR- don’t rip the frame and just put a thin molding behind the casing (between the wall and casing) that is stained the same color. Taking the casing off is not hard, just be careful not to dent the wood if you pry it off with a flat tool -OR- you can drive the finish nails trough the casing with a skinny nail set or punch and the casing will fall off. If you don’t know anyone with a table saw it would be dangerous to use anything else. With the casing off you can scribe a cut with a utility knife on the drywall of the perpendicular walls and dig out the drywall, slide the sides in, then head, nail finish nails and touch up the drywall. It looks the same when done, casing touches wall or wall touches casing.

Wow, that sounds like a lot of work. I’d install the door with 1/8" on each side, shim the finish molding to be flat, and call it a day. Caulk can hide a lot of sins…

Goofy has a power planer! And it doesn’t have to be completely clean … because there will be caulk/compound to cover up any imperfections.

In an earlier comment, he mentioned that 1/8" on each side won’t work in his configuration. So it’s 0 on one side and 1/4" on the other.

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