Doorway Trim Molding: Casing Sizes and Wall Layout
Doorway trim molding is the casing that frames a door opening: two side legs and a head piece, usually 2.25 to 3.5 in wide, set back 1/4 in from the jamb edge. If you are also adding panel molding to the wall, the casing becomes the anchor: frame gaps, frame heights and the plain strip beside the door all take their numbers from it.
Most guides to doorway trim stop at the casing itself: colonial or craftsman, mitered or butted, 2.25 or 3.5 in. That is the easy half. The half people get wrong is the wall around the door, where a frame lands 1 in from the casing, or a top rail sits 2 in above the head casing and looks like a mistake. This guide covers the casing basics briefly, then gives the layout rules, a clearance table and a worked 12 ft wall using our doorway trim molding companion kit, the pre-cut picture frame package with 60 to 120 cm frames.
Quick answer: Use 2.25 to 3.5 in casing for a standard 80 in (6 ft 8 in) door under an 8 ft ceiling, with a 1/4 in reveal. Keep wall frames 3 to 4 in from the casing edge and line the top of the upper frames up with the top of the head casing, about 82.75 in from the floor.
Key takeaways
- A 32 in door with 2.25 in casing and a 1/4 in reveal occupies 37.5 in of wall width from casing edge to casing edge.
- The top of the head casing on a standard 80 in door sits near 82.75 in; that is the line upper wall frames should share.
- Leave the strip between casing and corner plain when it is under 16 in (41 cm); a frame narrower than about 9 in reads as a stripe.
- Casing should be wider and at least as thick as the panel molding beside it: 2.25 in casing next to 1 in or 1.6 in frames keeps the hierarchy right.
- On a 12 ft wall with a door near one corner, two 41.3 in frame columns fill the open side for $136 in 1 in molding.
What is doorway trim molding, and which size do you need?
Doorway trim molding, also called door casing, covers the gap between the door jamb and the drywall. Interior casing is usually 2.25 in wide in standard homes, with 3.5 in common in newer or taller rooms. It is installed 1/4 in back from the jamb's inside edge, a step called the reveal.
The sizes below follow the common ceiling-to-casing pairing used by finish carpenters, for example in this casing style guide.
| Ceiling / door | Casing width | Wall frame molding that sits well beside it |
|---|---|---|
| 8 ft ceiling, 80 in door | 2.25 to 3.5 in (57 to 89 mm) | 1 in (25 mm) profile, or 1.6 in (40 mm) with 3.5 in casing |
| 9 ft ceiling, 96 in door | 3.5 to 4.5 in (89 to 114 mm) | 1.6 in (40 mm) profile |
| 10 ft ceiling and up | 4.5 in or built-up casing | 1.6 in profile, often nested double frames |
The hierarchy matters: casing is the frame of an opening, panel molding is decoration on a surface. If the wall frames are wider or chunkier than the casing, the door looks under-dressed. Our profiles are 25 x 13 mm and 40 x 20 mm; standard casing is about 11/16 in (17.5 mm) thick, so with the 40 x 20 mm profile keep the frames well away from the casing so the two never touch.
How far should wall molding sit from the door casing?
Use the same gap you use between frames, typically 3 to 4 in (7.5 to 10 cm), measured from the outer edge of the casing. Never less than 2 in: below that, the two caulk lines merge visually and the frame looks like it was squeezed in after the door was trimmed.
The strip between the casing and the room corner decides whether a frame fits at all. Here is the rule we use when we draw custom layouts, with 3.5 in gaps on both sides of each frame:
| Strip from casing to corner | Frames | Resulting frame width |
|---|---|---|
| Under 16 in (41 cm) | None, leave plain | Under 9 in, reads as a stripe |
| 16 to 28 in (41 to 71 cm) | 1 slim vertical frame | 9 to 21 in |
| 28 to 56 in (71 to 142 cm) | 1 frame | 21 to 49 in |
| 56 to 96 in (142 to 244 cm) | 2 frames | 22.75 to 42.75 in each |
| 96 to 140 in (244 to 356 cm) | 3 frames | 27.3 to 42 in each |
Formula: frame width = (strip width minus gaps) divided by frames, where gaps = frames + 1. Then round to the nearest stock width (60, 75, 90, 105 or 120 cm in our package) and let the leftover spread evenly across the gaps.
How high should frames go next to a doorway?
Line the top of the upper frames up with the top of the head casing. On a standard 80 in door with a 3/4 in head jamb and 2.25 in casing set 1/4 in back, the head casing tops out at about 82.75 in (210 cm). One shared horizontal line across the wall is what makes the trim look planned.
The calculation: 80 in door + 0.75 in jamb, minus the 0.25 in reveal = 80.5 in for the bottom of the head casing, plus 2.25 in casing width = 82.75 in. With 3.5 in casing the line moves to 84 in. Measure your own head casing rather than trusting the arithmetic: floors are rarely perfect.
- Upper frames: top edge on the head casing line.
- Lower frames: start one gap above the baseboard.
- Chair rail, if used: it dies into the casing side at its own height (32 to 36 in on an 8 ft ceiling) and needs the casing to be thicker than the rail, or the rail end must be returned.
Worked example: a 12 ft wall with a door near one corner
A 144 in (366 cm) wall, 8 ft ceiling, 4 in baseboard, a 32 in door whose casing starts 12 in from the left corner. The 12 in strip stays plain. The 94.5 in on the right takes two columns of 105 cm (41.3 in) frames with 4 in gaps, upper frames ending level with the head casing.
- Door footprint: 32 in door + 2 x 0.75 in jamb - 2 x 0.25 in reveal + 2 x 2.25 in casing = 37.5 in.
- Open wall: 144 - 12 - 37.5 = 94.5 in (240 cm) to the right of the casing.
- Frames: 2 columns of 41.3 in = 82.6 in; leftover 11.9 in / 3 gaps = 4.0 in (casing to frame, between frames, frame to corner).
- Heights: our package pairs a 55.1 in (140 cm) upper frame with a 17.7 in (45 cm) lower frame. With 3 in vertical gaps: lower frame from 7 to 24.7 in, upper frame from 27.7 to 82.8 in, level with the head casing.
- Molding length: per column 2 x (41.3 + 55.1) + 2 x (41.3 + 17.7) = 310.8 in; two columns = 51.8 ft (15.8 m).
- Cost: 2 sets at $68 in 1 in molding = $136, or $178 in the 1.6 in profile; $2.63 per linear foot in the 1 in version, $116 after WALL20.
- Switch check: a light switch usually sits 2 to 4 in from the latch-side casing at about 48 in high, right in the 4 in gap. A US plate is 2.75 in wide, so center it in the gap or move the first frame 1 in further out; never let a frame rail cut across the plate.
The vertical gap ends up at 3 in and the horizontal at 4 in. That difference is invisible at room scale; a top rail 2 in off the head casing line is not.
How do you install casing and wall molding in the right order?
Casing goes first, wall molding second. The casing fixes the reference lines (reveal, head height, outer edge), and the frames are measured off it. Paint can happen at the end for both, in one color for a built-in look or with the casing one shade deeper.
- Check the jamb is flush with the drywall; plane or shim before casing, or the casing will rock.
- Mark the 1/4 in reveal on the jambs and fix the casing with glue at the miters and finish nails.
- Snap a level line at the head casing top and transfer it across the wall with a laser.
- Mark the frame positions from the casing outward, starting with the first gap.
- Glue the pre-cut frames (or peel and press the self-adhesive version), top rail first, then sides, then bottom.
- Caulk the frame edges and the casing to wall joint, fill nail holes, then paint.
Pro tips
- Measure the head casing height on both sides of the door; if they differ by more than 1/8 in, set the frame line from the higher side and let the lower gap absorb it.
- On two doors on one wall, lay the frames out from the midpoint between the doors, not from the corners.
- If the door is dead center on the wall, mirror the frame layout exactly on both sides, even if one side has an outlet you need to work around.
- Paint the casing semi-gloss and the wall frames in the wall color and sheen; the opening reads as the strongest element, as it should.
- Where a chair rail meets the casing, cut the rail 1/16 in short and caulk; a tight fit pushes the casing leg out of line.
- Tape the full frame layout on the wall with painter's tape before gluing and look at it from the doorway of the next room.
Common mistakes with doorway trim and wall molding
- Frames almost touching the casing. A 1 in gap looks like an error. Fix: hold at least the frame-to-frame gap, minimum 2 in.
- Top rails that miss the head casing line by an inch or two. Fix: set the upper frame top to the measured casing top and adjust the vertical gaps instead.
- A narrow frame squeezed into a 12 in strip. Fix: under 16 in, leave the strip plain or carry only the chair rail across it.
- Panel molding wider than the casing. Fix: use the 1 in profile next to 2.25 in casing, or upgrade the casing to 3.5 in before adding 1.6 in frames.
Shop the look
- Picture Frame Wainscoting Kit: 1 to 5 panels, handy for the short wall between a door and a corner, from $51.25.
- Wall Molding Kit with Chair Rail: 3 upper and 3 bottom frames plus rail for a hallway wall with a door, $165 to $197.
- Half Wall Wainscoting Kit with 6 cm Chair Rail: lower frames only, sold by panel count from $39.41, when the upper wall stays plain.
We do not sell door casing itself; buy it locally in the width from the first table, and use our kits for the wall around it.
Frequently asked questions
What is the difference between trim and molding?
Molding is a shaped strip; trim is the job it does, covering joints such as door casing and baseboard. In practice the words overlap, and door casing is both.
Should baseboard trim match door trim?
They should share a style, not a size. Casing is normally a little thicker than the baseboard so the baseboard ends neatly against it.
How do you put trim on a doorway without a door?
The same way: a jamb or drywall return first, then casing on both faces with a 1/4 in reveal. A cased opening often takes 3.5 in casing to look substantial.
Is there peel and stick door trim molding?
Self-adhesive casing exists, but a door frame takes knocks every day, so we recommend glue and finish nails for casing. Self-adhesive frames work well on the wall around it.
How much does doorway trim molding cost?
Paint-grade casing runs roughly $1 to $2.50 per linear foot, according to Bob Vila's casing guide, and a standard door needs about 17 ft per side. The wall frames in our example add $136.
For depth and size rules across the whole room, read our guide to architectural trim by ceiling height. Ready to choose? Browse Wall Molding Kits, or plan your wall with live pricing in our Wall Designer.
Last updated: October 8, 2026
