Miter Angle Calculator
Find the right miter for any joint. Enter a corner angle in degrees (walls are rarely a true 90), or the number of sides for a frame or planter, and get the true miter angle plus the setting to dial on a miter saw.
Example: with Solve from Corner angle (measured) · Corner angle (deg) 135 · Number of sides 6 → Miter angle (per piece): 67.50° from the face of each piece.
- Miter saw setting22.50° from square
- Corner angle used135.00° corner (as entered)
Computed by the calculator below using its default values. Change any input to see your own numbers.
Each piece is cut to half the corner angle. Saw scales read from square (0° = a 90° cut), so the saw setting is 90 minus the half angle — 45 on the dial for a square corner.
Half the corner, every time
A mitered joint splits the corner angle equally between the two pieces, so each piece is cut at half the corner angle. A square 90° corner takes two 45° cuts; a 135° bay-window corner takes two 67.5° cuts. For frames and planters the corner angle comes from geometry: an n-sided polygon has interior angles of (n − 2) × 180 ÷ n, so a hexagon planter (120° corners) needs 60° miters.
The confusion is the saw scale. Miter saws read 0° at a square crosscut, so the dial setting is 90 minus the miter angle: that hexagon's 60° miter is 30° on the saw. Settings past about 50° do not exist on the scale — for sharper cuts, flip the workpiece against the fence or build a simple angled jig.
How it’s calculated
Miter angle = corner angle ÷ 2. Saw setting = 90° − miter angle (saw scales measure deviation from a square cut). Polygon mode: interior corner angle = (n − 2) × 180 ÷ n for n sides, so the saw setting equals 180 ÷ n — 45° for a square, 30° for a hexagon, 22.5° for an octagon.
Assumes both pieces meet in the same flat plane — sloped crown molding or tilted work needs a compound miter with a bevel component this page does not compute.
Miter settings for common shapes
| Shape / corner | Corner angle | Miter per piece | Saw setting |
|---|---|---|---|
| Square frame (4 sides) | 90° | 45° | 45° |
| Pentagon (5) | 108° | 54° | 36° |
| Hexagon (6) | 120° | 60° | 30° |
| Octagon (8) | 135° | 67.5° | 22.5° |
| Bay window corner | 135° | 67.5° | 22.5° |
| Out-of-square wall | 92° | 46° | 44° |
Computed with miter = corner ÷ 2 and saw = 90 − miter; polygon corners from (n − 2) × 180 ÷ n.
Common mistakes
- Dialing the miter angle itself into the saw — the scale reads from square, so a 60° miter is cut at 30 on the dial.
- Assuming walls are 90°: drywall corners commonly run 88–92°, and splitting the measured angle is what closes the gap.
- Measuring the outside corner but cutting for the inside one — the two angles are supplements (they add to 180°).
- Using miter-only settings for crown molding laid flat against the fence; sprung crown needs compound (miter + bevel) angles.
Frequently asked questions
How do I calculate a miter angle?
Divide the corner angle by two — each piece takes half. A 135° corner needs 67.5° miters. On the saw, set 90 minus that: 22.5° from square.
Why is my miter saw setting different from the miter angle?
Saw scales define 0° as a straight crosscut, while the miter angle is measured from the board's face. They always add to 90: a 60° miter is 30° on the saw.
What angle do I cut for a hexagon?
A hexagon's interior corners are 120°, so each piece is mitered at 60°, which is 30° on the saw dial. In general the saw setting for an n-sided frame is 180 ÷ n.
How do I handle a wall corner that is not square?
Measure it with a digital protractor or angle finder and enter the actual reading. A 92° corner wants 46° miters (44° on the saw); splitting the true angle keeps both reveal lines even.