Miter and Bevel Cut Calculator
Computes the exact miter and bevel angles for picture frames, polygon frames, and crown molding joints. Use it before setting your miter saw to avoid costly cut errors on expensive molding stock.
Last updated: September 2026
Formula below · 2 sources (fpl.fs.usda.gov, Wikipedia) · Updated Sep 2026
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About this calculator
For a simple corner joint, the two pieces split the corner evenly, so the miter saw setting (measured from a square crosscut) is (180° − cornerAngle) / 2: 45° for a 90° corner, 30° for a 120° corner and 22.5° for a 135° corner. For a regular polygon frame with N sides the corners are all equal and the setting is 180° / N (the 'Compound' option). Crown molding laid flat on the saw needs a compound cut; the miter setting is: miter = atan(sin(springAngle) / tan(cornerAngle / 2)), and the matching bevel is asin(cos(springAngle) × cos(cornerAngle / 2)). Here the spring angle is the angle between the back of the molding and the wall (38° for standard 52/38 crown, 45° for 45/45 crown). For a 90° corner that gives 31.6° miter and 33.9° bevel for 52/38 crown, and 35.3° miter and 30° bevel for 45/45 crown. This calculator returns the miter setting; set the bevel from the formula above.
How to use
Example: cutting a regular octagon (8-sided) frame. Choose Compound and enter sides = 8: miter = 180 / 8 = 22.5°. Set the saw to 22.5° and cut both ends of all 8 pieces as mirror cuts; they close into an octagon. Example: crown molding on a 90° inside corner with 52/38 crown. Choose Crown Molding, spring angle 38 and corner 90°: miter = atan(sin 38° / tan 45°) = atan(0.616) = 31.6°; set the bevel to asin(cos 38° × cos 45°) = 33.9°. The same corner with a simple flat miter is (180 − 90) / 2 = 45°.
Frequently asked questions
How do I find the miter angle for a picture frame with a 90-degree corner?
For a standard 90° corner, the formula simplifies to (180 − 90) / 2 = 45°, so each piece is cut at 45° on both ends. This is the most common miter cut in woodworking and is why a 45° stop is standard on every miter saw. Both pieces are identical, which makes setting up a stop block for repeatable cuts very easy. Always make a test cut in scrap first and check the joint closes tightly before cutting your finished material.
What is the spring angle for crown molding and how does it affect saw settings?
The spring angle is the angle at which crown molding rests against a flat wall — typically 38° or 45° for standard profiles. It matters because crown molding is a compound joint: the wall corner angle and the spring angle together determine both the miter and bevel settings on your saw. A 45° spring angle simplifies the math and is friendlier for cutting crown flat on the saw table. If your molding has an unusual spring angle, measure it by holding the molding against a flat surface and measuring the angle it makes with the surface.
Why do compound miter cuts require both a miter angle and a bevel angle simultaneously?
Crown molding and similar trim pieces sit at an angle relative to both the wall and the ceiling, meaning the joint exists in three-dimensional space rather than a flat plane. A single flat miter cut would leave a gap because it doesn't account for the tilt of the molding. By tilting the blade (bevel) and rotating the fence (miter) at the same time, you effectively project the true joint angle onto both the face and edge of the board. Getting either setting wrong, even by a degree, results in a visible gap that is difficult to fill cleanly.