Miter Angle Calculator
The miter saw setting for a frame with any number of sides or for any corner, with the cut angle and the inside length of each frame piece.
Result
45 °
Away from a square cut, as the saw scale readsAngles are exact; cut a test joint in scrap before cutting the good stock.
- Angle between the cut and the board edge
- 45 °
- Corner angle
- 90 °
- Inside length of each side
- 8 in
https://calcgallery.com/lumber-carpentry/miter-angle-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Miter Angle Calculator
- Choose a frame with equal sides, or one corner.
- For a frame, enter the number of sides, and the outside length and width of each piece if you want the inside length.
- For one corner, enter the angle between the two pieces where they meet.
- Set the saw to the miter setting shown and cut both pieces at it, one to the left and one to the right.
How it is calculated
corner angle = 180° × (sides − 2) ÷ sides for a frame with equal sidessaw setting = 90° − corner angle ÷ 2 = 180° ÷ sides for a framecut angle = corner angle ÷ 2inside length = outside length − 2 × width ÷ tan(corner angle ÷ 2)A miter joint splits its corner in two, so each piece takes half. The saw setting is that half measured from a square cut, which is how the scale on most miter saws reads.
Cutting tips
Cut a test joint in scrap first. A saw that is a fraction of a degree off opens a gap that is multiplied by every corner of a frame: on an eight-sided frame the error appears sixteen times. When a joint opens on the outside, the angle is too large; on the inside, too small. This page covers flat miters. Crown moulding set at a spring angle needs a compound miter, with a bevel as well as a miter setting, which is not calculated here.
With your numbers
- Corner = 180° × (4 − 2) ÷ 4 = 90 °
- Saw setting = 90° − 90 ° ÷ 2 = 45 °
Quick reference
Angles are exact; cut a test joint in scrap before cutting the good stock.
| Job | Miter saw setting |
|---|---|
| Square frame | 45 ° |
| Triangle | 60 ° |
| Hexagon | 30 ° |
| Octagon | 22.5 ° |
| 135° bay window corner | 22.5 ° |
| 100° corner | 40 ° |
| Square frame, 30 cm | 45 ° |
Common questions about the Miter Angle Calculator
- What angle do I cut for a hexagon?
- Set the saw to 30°. A hexagon has six corners of 120°, and each piece is cut at half of that measured from its edge, 60°, which is 30° away from a square cut. For any frame with equal sides, the saw setting is 180° divided by the number of sides.
- Why are there two angles?
- They describe the same cut from different starting points. Most miter saws read 0° for a square cut, so the saw setting is how far to swing away from square. The cut angle is measured between the cut and the long edge of the board, which is how a protractor or a speed square reads it. They always add up to 90°.
- My wall corner is not exactly 90°. What do I cut?
- Measure the corner with an angle finder, choose one corner and enter it. A corner of 92° needs a saw setting of 44°, one degree less on each piece than a square corner would take.
- How long is the inside edge of each frame piece?
- The outside length less twice the moulding width divided by the tangent of half the corner. On a square frame that is simply the outside length less twice the width: 12 inch sides of 2 inch moulding are 8 inches on the inside.