What miter for a corner that isn't 90 degrees?
Half the angle left over from a straight line: a 92° corner is cut at 44°, not 45°. The rule, a table of measured corners, and how to measure the corner you actually have.
Cut each piece at half of what is left from 180° — a 92° corner takes 44.0° per side, not 45.0°.
The two pieces split the joint between them, so each one is cut at (180 − corner) ÷ 2. Getting this right is the difference between a trim job that looks sharp and one that looks approximate.
How that is worked out
- Flat trim — baseboard, casing, chair rail — never leaves the plane of the wall, so the joint is only ever a miter. No bevel, no compound anything.
- The two halves of the joint have to add up to the turn the corner makes, and they split it evenly: (180 − corner) ÷ 2 each.
- A 90° corner gives 45.0°, which is why 45 is the number everyone knows. A 92° corner gives 44.0° — one degree, and visible across a room as a wedge of daylight at the top of the joint.
Miter per side, by the corner you measured
| Measured corner | Miter per side | Off 45° |
|---|---|---|
| 85° | 47.5° | +2.5° |
| 88° | 46.0° | +1.0° |
| 89° | 45.5° | +0.5° |
| 90° | 45.0° | 0.0° |
| 91° | 44.5° | -0.5° |
| 92° | 44.0° | -1.0° |
| 95° | 42.5° | -2.5° |
| 135° | 22.5° | -22.5° |
Worth knowing
- Measure the corner rather than assuming it. A bevel gauge held against both walls and read on a protractor takes ten seconds; a digital angle finder does it directly. Drywall corners are routinely a degree or two out and a corner with built-up compound in it can be worse.
- Measure at the height the trim sits, not at eye level. A bowed wall gives a different angle at the floor than at the ceiling, and baseboard cares about the floor.
- Split the difference on a wall that changes along its length: cut the joint for the angle at the joint, and let the flat of the board bridge the rest.
- This is flat trim only. Crown leans out from the wall and needs a miter and a bevel together — that is the crown molding calculator.
Work out your own numbers
- Miter angle calculator
The miter for baseboard, casing or chair rail at any corner angle — flat trim, so there's no bevel to set.
- Baseboard calculator
Linear footage of flat trim for a room from its perimeter and its doorways, with a waste allowance.
- Crown molding angles
The miter and bevel for any corner and any spring angle, plus the single setting for cutting it nested.
Related questions
- How do I find the angle of a corner?
- Hold a sliding bevel gauge against both wall faces, lock it, and read it on a protractor — or use a digital angle finder, which gives the number directly. Do it at the height the trim will sit. What you want is the angle between the two wall faces, which is what the table above is indexed on.
- My corner is 91 degrees. What do I cut?
- 44.5° on each piece. The rule is (180 − 91) ÷ 2. Most miter saws will not hold a half degree reliably off the detent, so nudge past the 45 detent and cut a test pair from offcuts before committing to the real trim.
- Should I cope or miter an inside corner?
- Cope, if the trim profile allows it and the house is likely to move. A coped joint has one piece running into the corner and the other cut to its profile, so the joint closes up as things shift instead of opening. Miter outside corners — there is no coping them — and miter inside corners in a stable, square opening where speed matters more.