The short answer
Jamb width should equal the finished wall thickness: stud depth plus the drywall on both sides. A 2×4 wall with ½″ drywall on each side is 4-1/2″ thick and takes a 4-9/16″ jamb. A 2×6 wall with ½″ drywall is 6-1/2″ and takes a 6-9/16″ jamb. The extra 1/16″ leaves room for the drywall to vary.
Common wall types and jamb widths
| Wall | Finished thickness | Jamb to order |
|---|---|---|
| 2×4 studs, ½″ drywall both sides | 4-1/2″ | 4-9/16″ |
| 2×4 studs, ⅝″ drywall both sides | 4-3/4″ | 4-13/16″ or wider |
| 2×6 studs, ½″ drywall both sides | 6-1/2″ | 6-9/16″ |
| 2×6 studs, ⅝″ drywall both sides | 6-3/4″ | 6-13/16″ or wider |
The formula is simple: stud depth + total drywall + 1/16″. A 2×4 is 3-1/2″ deep and a 2×6 is 5-1/2″.
Why it matters on multi-unit jobs
Most suite partitions are 2×4 with ½″ drywall, so 4-9/16″ covers the bulk of the doors. The exceptions are where jobs go wrong:
- Plumbing walls are often framed with 2×6 to fit drain lines, so bathroom doors may need 6-9/16″ jambs.
- Walls with ⅝″ Type X drywall, used where fire ratings apply, are a quarter inch thicker than standard.
- Walls with resilient channel or sound bars for acoustic separation add their own thickness.
A jamb that’s too narrow leaves the casing sitting proud of the drywall, and carpenters end up ripping and gluing extension strips onto every door. A jamb that’s too wide has to be planed down. Either way, it’s labour you’re paying for twice.
How to get it right
- List the wall types on the plans. Note stud size, drywall thickness and any channel or furring for each.
- Match each door to its wall. Mark which openings sit in which wall type.
- Measure on site if framing changed. Measure the finished wall at the opening, drywall to drywall, before ordering a late phase.
- Send it with the door schedule. We’ll price the jamb widths per opening, so the doors arrive ready to set.
Our standard prehung jamb is 4-9/16″ finger-jointed pine. Other widths are made to order.
Sources
Code requirements change and local rules vary. Confirm sizes and clearances with your designer and building department before ordering. We supply doors and trim; we’re not a code consultant.
