Skip to tool content
Toolioz logoToolioz

Miter Angle Calculator

A miter angle calculator for regular polygons uses 180°/n as the saw angle from square. Picture frames are half the corner. Compound crown uses miter = atan(sin(spring)×tan(corner/2)) and bevel = asin(cos(spring)×sin(corner/2)).

Quick Summary & Direct Answer
Home

What miter is an octagon?

Eight sides: 180/8 = 22.5° miter. Interior angle is 135°. A 90° frame is a 45° miter. Crown at 38° spring into a 90° corner is about 31.6° miter and 33.9° bevel.

Key Takeaways

  • Polygon miter is 180/n.
  • Frames: half the corner.
  • Compound needs spring angle from the wall.

8-gon miter

22.5°

Interior135°
Frame miter45°
Compound miter31.62°
Compound bevel33.86°

Results can be wrong. This calculator is unofficial. Figures can be incomplete, rounded, or not updated. Use them at your own risk and check a tape, datasheet, ball band, or official chart before cutting, mixing, buying, or publishing. Compound crown numbers use spring angle from the wall. A saw’s bevel/miter scale and a nested vs flat cut can read the complement of these angles. Limits of liability are in the terms of service.

Frequently asked questions

180/6 = 30°.

Explore Related Tools

Board Feet Calculator

Counts lumber board feet and log scale with Doyle, Scribner, and International ¼″.

Try tool

Wallpaper Calculator

Estimates rolls with pattern repeat, straight match, or half-drop.

Try tool

Aquarium Volume Calculator

Finds litres and gallons for rectangular, bowfront, cylinder, hexagon, and corner tanks.

Try tool

Publisher notes · reviewed 29 October 2026

Polygon miter is 180 divided by n

Octagon 22.5°. Frame miter is half the corner. Compound crown: miter = atan(sin(spring)×tan(corner/2)), bevel = asin(cos(spring)×sin(corner/2)). Confirm whether a saw scale reads from square.

Spring angle

38° and 45° are common crown springs. Measure the lean off the wall, not the room corner.

Worked examples

  • Octagon

    22.5° miter, 135° interior.

Limits of this page

  • Coped joints are not computed.
  • Compound identities assume a square room unless corner is changed.

Sources