Compound Miter Calculator
When the sides tilt — crown molding, a splayed planter, a hopper — a flat miter won't close the joint. You need a miter and a bevel together. Get both saw settings for any spring angle, corner, or number of sloped sides.
The angle between the wall and the back of the crown. It's printed on the molding or its packaging.
90° for a normal square inside corner.
0° = straight vertical sides (a flat miter). Larger tilt = more splay, and a bigger bevel.
Formula & how it works
For crown at spring angle S and wall corner C, the flat-cut settings are miter = atan(sin S × tan(C/2)) and bevel = asin(cos S × sin(C/2)).
For a sloped box of N sides tilted φ from vertical, miter = atan(cos φ × tan(180/N)) and bevel = asin(sin φ × cos(180/N)). With vertical sides (φ = 0) the bevel is zero and the miter reduces to the flat 180/N.
Worked example
A standard 52/38 crown (38° spring) on an inside 90° corner: miter ≈ 31.6°, bevel ≈ 33.9°. Switch to a 45/45 crown and it becomes 35.3° miter, 30° bevel.
Cutting compound angles
Flat on the saw, not nested
These figures are for cutting the molding lying flat on the saw table with the blade both swung and tilted. The alternative — holding crown nested against the fence at its spring angle — uses a plain miter instead, and mixing the two methods is a common source of ruined pieces.
Direction is the hard part
The angles are only half the job; which way to swing the miter and tilt the bevel depends on whether it is an inside or outside corner and which end of the piece you are cutting. Label your scraps left and right and dry-fit before committing.
Spring angle changes everything
Crown is sold in different spring angles, and using the wrong one throws both settings off. Confirm your molding's spring angle — it is usually the smaller number in a pair like 52/38 — before you cut.