Miter angle calculator

How the saw settings are worked out

Flat frames and trim

Two pieces meeting at a corner each turn half of the change in direction. A square corner is a 90° turn, so each piece is cut at 45°. For a closed frame with n equal sides, each cut is 180° ÷ n: 60° for a triangle, 36° for a pentagon, 30° for a hexagon and 22.5° for an octagon. For a corner that is not square, measure it first and enter the real angle.

Crown molding and sloped sides

Crown molding leans out from the wall, and the sides of a planter or hopper lean out from vertical, so the cut has to tilt as well as turn: a compound cut with both a miter and a bevel. With h as half the turn at the corner and t as how far the face leans from vertical, the calculator uses bevel = arcsin(sin h × cos t) and miter = arctan(tan h × sin t).

Example: standard 52/38 crown on a square wall corner needs a miter of 31.62° and a bevel of 33.86°; 45/45 crown needs 35.26° and 30.00°. Those match the published crown tables, and the same numbers serve both sides of the corner, with the miter swung the other way for the second piece.

Reading your saw

• Most miter saws read 0° for a square cut, which is how this page gives its numbers. Some gauges read 90° when square; the page shows that reading too.
• Saw detents are often a fraction of a degree out. Cut two scraps, put them together and check the joint against a square before cutting good stock.
• Crown can also be cut nested, standing upside down against the fence at its spring angle, which needs only a miter. The page gives that setting as well.