Door Frame Materials Calculator
Calculate jamb, casing, and shim materials from rough opening size.
Returns linear feet and a cut list for interior and exterior door frame installations.
Door framing involves three distinct phases: the structural rough opening in the wall framing, the finish jamb that lines the opening, and the decorative casing that trims both sides of the finished wall.
Rough opening size (structural framing):
Rough Opening Width = Door Width + 2 inches (for jamb + clearance)
Rough Opening Height = Door Height + 2.5 inches (for jamb, threshold, and clearance)
Standard door rough openings:
| Door Width | Door Height | Rough Width | Rough Height |
|---|---|---|---|
| 24" (2'0") | 80" (6'8") | 26" | 82.5" |
| 28" (2'4") | 80" (6'8") | 30" | 82.5" |
| 30" (2'6") | 80" (6'8") | 32" | 82.5" |
| 32" (2'8") | 80" (6'8") | 34" | 82.5" |
| 36" (3'0") | 80" (6'8") | 38" | 82.5" |
| 36" (3'0") | 96" (8'0") | 38" | 98.5" |
Finish jamb components:
The jamb is a three-sided box that drops into the rough opening, so every piece of it has to be smaller than the hole, never larger. The side legs run the full height and the head jamb butts between them.
Side Jamb Length = Rough Opening Height − 1/4" shim gap at the head
Head Jamb Length = Rough Opening Width − 2 × Jamb Thickness − 1/2" total shim gap
That is the piece most cut lists get backwards. A head jamb worked out as the opening width plus two jamb thicknesses is an inch and a half longer than the hole it is supposed to fit inside, and you find that out with the saw already put away.
Standard jamb thickness = 1-1/16 inch (27 mm) for 4-9/16" wall or 1-3/8" for thicker walls. Jamb width must match your wall thickness: 4-9/16" for 2×4 construction + drywall, 6-9/16" for 2×6 construction.
Casing / trim components: Casing is installed on both faces of the wall around the door.
Side Casing Length = Rough Opening Height + Reveal + Miter Allowance (add ~3")
Head Casing Length = Rough Opening Width + 2 × Reveal + Miter Allowance (add ~6")
Both are measured from the opening, not from the door, which is what the calculator below asks for.
Reveal = the visible setback from the jamb edge, typically 3/16"–1/4" (5–6 mm).
Shim pairs: Shims are used to plumb and level the jamb within the rough opening. Set a pair no more than 16 inches apart down each side jamb, which works out to 7 pairs per side in a standard 82.5-inch opening, plus a pair at each top corner. That is more than many carpenters use, and it is deliberate. Shims cost pennies and a long jamb left unsupported between the hinges will bow in a season or two, at which point the door stops latching.
Materials list for a standard 32"×80" interior door (34" × 82.5" rough opening):
| Item | Quantity |
|---|---|
| Side jambs | 2 × ~82-1/4" lengths |
| Head jamb | 1 × ~32" length |
| Side casings | 2 × ~85-3/4" per face |
| Head casing | 1 × ~40-1/2" per face |
| Shim pairs | ~16 pairs |
| Door stop (optional) | 3 pieces (2 sides + head) |
The head casing runs long on purpose. It has to cover the opening plus a reveal on each side plus the width of both side casings it mitres into, so cutting it to the door width leaves you short by the better part of six inches.
Pre-hung versus build-in-place. Pre-hung doors, with the slab already mounted in the jamb assembly, cost more but eliminate most of this measuring and cutting. Unless you are matching an odd old opening or a jamb width nobody stocks, buy the pre-hung.
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