A miter angle splits a corner so two pieces meet cleanly. The right saw setting depends on the corner angle, the number of sides, and how the material sits against the saw.
Simple Corners
For a square frame corner of 90 degrees, each mating piece is commonly cut at 45 degrees.
For other corner angles, divide the corner angle by two to estimate the matching miter.
Polygons and Trim
Regular polygons use equal outside angles, so the miter can be calculated from the number of sides.
Trim work can be more complex because walls are rarely perfect and compound angles may be involved.
Miter Angle Formula
For a simple corner, miter cut angle = corner_angle / 2. A 90 degree corner gives a 45 degree miter.
For a regular polygon, miter cut angle = 180 / number_of_sides. The saw complement angle is 90 minus the miter cut angle.
Worked Example
A four-sided frame has 90 degree corners, so each miter cut is 45 degrees.
A six-sided regular frame uses 180 / 6 = 30 degrees for the miter cut from square.
Common Mistakes
Do not confuse miter angle with bevel angle. A miter turns across the face; a bevel tilts through the thickness.
Check the saw scale convention and make test cuts, especially when walls, frames, or lumber/timber pieces are not perfectly square.
FAQs
Why do miters need test cuts?
Real corners, saw calibration, blade deflection, and material movement can all affect the final fit.
Is a miter angle the same as a bevel angle?
No. A miter turns across the face of the material, while a bevel tilts through the thickness.
Estimates only
These results are estimates only. Verify measurements, material specifications, structural requirements, safety requirements, and local building rules before buying materials or building.