Picture Frame Miter Angle Calculator
Calculate the miter (chop saw bevel) angle needed for each corner of an equal-sided frame, box, or polygon project.
How the angle is worked out
Two mitred ends meet to form one corner, so each piece takes half the turn:
interior angle = (sides - 2) × 180 / sides
miter angle = 90 - interior angle / 2 (which is 180 / sides)The default of 4 sides gives a 90° interior corner and a 45° miter: two 45° cuts close a square frame. Six sides gives 120° and 30° miters, eight gives 135° and 22.5°. The answer is the angle read off a miter saw's scale, which is measured from a square crosscut, not from the fence. Sides are taken as a whole number of 3 or more - 7.5 is truncated to 7.
| Sides | Interior | Miter each end |
|---|---|---|
| 3 | 60° | 60° |
| 4 | 90° | 45° |
| 6 | 120° | 30° |
| 8 | 135° | 22.5° |
Why a correct angle still leaves gaps
Error multiplies by the number of cuts. A saw half a degree off closes a square frame four degrees out of true across eight cuts, and an octagon eight. Check the saw against a known square before the frame stock, cut test pieces in scrap of the same thickness, and adjust by half the gap you see - each end owns half the corner. Grain matters too: mitred end grain drinks glue, so size the joint with thinned glue first or reinforce the corner with a spline or a V-nail rather than trusting the glue line.
Frequently asked questions
What miter angle do I cut for a hexagon frame?
30° at every end. Six pieces, twelve cuts, and each 120° corner is two 30° faces meeting.
Can a miter saw cut the 60° a triangle needs?
Most stop at 50-60°, and many bind before they get there. Cut triangles on a table-saw sled or a tapering jig, or set 30° and run the stock against a square support instead.
Is the miter angle the same as the bevel angle?
Not for a tilted-side box. This assumes flat frame pieces standing square to the table. Splayed sides need a compound setting, where the miter and the bevel both shift away from these numbers.