Each cut is half the corner
Two pieces meeting at a corner each carry half the turn. A 90° corner needs two 45° cuts; a picture frame corner is the same. For a many-sided frame the inside corner angle is (sides − 2) × 180 ÷ sides, and the miter is half of that.
Miter angle by corner
| Shape | Corner angle | Miter cut (each piece) |
|---|---|---|
| Triangle (3 sides) | 60° | 30° |
| Square (4 sides) | 90° | 45° |
| Pentagon (5 sides) | 108° | 54° |
| Hexagon (6 sides) | 120° | 60° |
| Octagon (8 sides) | 135° | 67.5° |
The saw setting for a right-angle corner is 45°. For an octagon it is 67.5°, which is past the usual 45° stop, so you swing the saw the other way and cut it as a 22.5° setting from square.
The two ways a corner can be off
- Corners that are not square. Walls rarely meet at exactly 90°. Measure the real corner angle and halve it, rather than assuming 45°.
- Miter is not bevel. A miter swings the blade left or right across the face; a bevel tilts it through the thickness. A compound cut does both at once, which is what crown molding needs.
Common questions
What miter angle do I cut for a 90-degree corner?
Each piece is cut at 45 degrees. The two 45-degree cuts meet to close the 90-degree corner exactly.
What is the miter angle for a hexagon?
A hexagon has 120-degree inside corners, so each cut is 60 degrees. For any regular shape, the miter is 180 minus the corner angle, divided by 2.
Is the miter angle the same as the saw setting?
Usually yes on a miter saw, whose scale reads zero for a straight cut and 45 for a right-angle corner. But some saws are marked with the complementary angle, so a 45-degree cut reads as 45 either way only because the corner is symmetric. For other corners, check whether your scale measures from the fence or from square.
