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Compound Miter Angle Calculator
Get the correct miter angle for any regular-sided frame or box, plus the compound miter and bevel angles crown molding needs to close a clean corner.
Plain miters: 180 divided by the sides
For a picture frame, box or any shape with equal straight corners, the miter angle to set on the saw is always 180° divided by the number of sides — 45° for a 4-sided rectangular frame, 30° for a hexagon, and so on, so the two mating pieces meet exactly at the shape's corner angle.
Crown molding needs two angles at once
Crown molding is installed tilted between the wall and ceiling, described by its spring angle. Cutting it flat on the saw table (rather than tilted against a jig) needs a compound cut — a miter angle from turning the table and a bevel angle from tilting the blade — worked out here from the spring angle and the number of sides using standard compound-miter trigonometry.
Frequently asked questions
Why is the miter angle for a 4-sided frame 45°?
For a shape with straight corners, the miter angle is always 180 divided by the number of sides. A rectangular frame has 4 sides, so each piece is cut at 180 ÷ 4 = 45° so the two mating angles add up to a clean 90° corner.
What is a spring angle and why does it matter for crown molding?
Crown molding is installed tilted between the wall and ceiling rather than flat, and the spring angle describes that tilt (commonly 38° or 45°). Because the molding sits at an angle, cutting it flat on the saw table needs both a miter (table turn) and a bevel (blade tilt) to make the joint line up.
Can I cut crown molding without tilting the blade?
Yes — many people prefer cutting crown molding upside-down and 'nested' against the fence and table exactly as it will sit on the wall, using only the miter angle and no bevel at all. The compound angles here are for the alternative method of cutting it flat on the table.
Do these angles work for any room corner, not just 90°?
This calculator assumes a regular shape with equal corners, like a standard rectangular frame or room. An out-of-square wall corner needs its actual angle measured on site and the miter split accordingly, which this tool does not account for.