What is the rough opening size for a door?
Slab width plus 2", slab height plus 2" to 2 1/2" — a 2'8" door wants roughly a 34" by 82" hole. A framing convention, not a standard; check the actual unit before you frame.
A 2' 8" × 6' 8" door wants a rough opening about 34" wide by 82" to 82 1/2" tall.
That is the framing convention, not a number from the door itself — the actual unit's own instructions, once you have them, override this every time.
How that is worked out
- Add 2" to the door slab's width — an inch of shim space on each side of the jamb.
- Add 2" to 2 1/2" to the slab height, for the head jamb, shims above it, and room under the sill for the finished floor.
- A 32" × 80" slab becomes roughly 34" × 82"–82 1/2" of framed opening.
Rough opening by standard slab size
| Door size | Rough opening width | Rough opening height |
|---|---|---|
| 2' × 6' 8" | 26" | 82" – 82 1/2" |
| 2' 4" × 6' 8" | 30" | 82" – 82 1/2" |
| 2' 6" × 6' 8" | 32" | 82" – 82 1/2" |
| 2' 8" × 6' 8" | 34" | 82" – 82 1/2" |
| 2' 10" × 6' 8" | 36" | 82" – 82 1/2" |
| 3' × 6' 8" | 38" | 82" – 82 1/2" |
Worth knowing
- This is a framing convention, not a standard the way PS 20 sets dressed lumber sizes. Every door manufacturer publishes its own rough-opening spec for its own units — pre-hung doors, in particular, vary by jamb width and by whether the maker builds in extra shim allowance.
- Framing before the door is chosen is common on new construction, and this is what to frame to. Once the door arrives, its own instruction sheet is authoritative — build to it, not to this rule, if the two disagree.
- Exterior doors add a sill and often a wider jamb for insulation, which changes both numbers. This convention is closest for interior doors and ordinary pre-hung exterior units.
- A rough opening that is too generous is easy to shim down to plumb and square. One that is too tight means pulling framing back out — err toward the larger figure if you must guess before the unit is on site.
Work out your own numbers
- Wall framing stud count
Field studs at 16" or 24" on centre, corner studs, and the king and jack studs every opening adds.
Related questions
- What size rough opening for a 32 inch door?
- About 34" wide by 82" to 82 1/2" tall, using the standard framing allowance of 2" on width and 2" to 2 1/2" on height. That is a starting point for framing before the door arrives — the actual unit's spec sheet, once you have it, is the number to build to.
- Why is the rough opening bigger than the door?
- Because the door slab has to fit inside a jamb, and the jamb has to be shimmed plumb and square inside the framed opening — none of that fits if the hole is cut to the exact size of the door. The extra 2" of width and 2" to 2 1/2" of height is room for the jamb and the shims around it.
- Is the rough opening size the same for every door brand?
- No. It is a widely used convention, not a standard like dressed lumber sizes — jamb thickness, whether the unit is pre-hung, and the maker's own shim allowance all move the number slightly. Framing to this rule before the door is chosen is normal; once you have the actual unit, its instructions govern.