Mitre joint
A mitre joint cuts two pieces at matching angles to form a corner, 45 degrees for a square one. When to mitre and when to scribe instead.
Ask Chalkline about this →A mitre joint is a joint where two pieces are each cut at an angle so they meet to form a corner, the cut on each piece being half the corner angle. For a square (90 degree) external corner, each piece is cut at 45 degrees. It is the standard way to turn architrave and skirting around an external corner, and to frame the picture-frame architrave around a door or window.
How it is done
- Cut to half the angle. A drop saw set to 45 degrees gives the two halves of a 90 degree corner. Out-of-square walls need the angle adjusted (a 92 degree corner is two 46 degree cuts).
- Glue and fix. The faces are glued (PVA or an adhesive) and the joint pinned or nailed so the two pieces stay tight and cannot creep apart.
- External corners and closed frames. That is where the mitre belongs (see skirting and architrave install).
Mitre vs scribe
Internal corners are usually scribed (also called coped), not mitred. The first piece runs into the corner square; the second is cut to the reverse profile of the first so it sits neatly over it.
The reason is movement: an internal mitre opens into an ugly gap as the timber shrinks or if the corner is not dead square, whereas a scribed joint hides that movement and holds the line. So the rule of thumb is mitre the external corners, scribe the internal ones.
A mitre also shows on cornice external corners and any framed moulding.
Also known as: mitred joint, 45-degree joint, mitre.
Category: Carpentry / joinery
Related
See also
Last updated: 2026-05-26. Verified: 2026-05-26. Quarterly review for currency.