Miter Angle Calculator
Calculate miter and bevel angles for corners and crown molding.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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This calculator gives you the exact miter (and bevel) angle to set on your saw for any corner or crown molding installation. Here is how to use it:
- Enter your corner angle. For a standard room corner, use 90 degrees. For a bay window or other non-square corner, measure the actual angle between the two walls. A typical bay window uses 135 degrees (forming a 45-degree offset), and an octagonal room uses 135 degrees as well.
- Choose your mode. Select Simple Miter for baseboards, door casings, picture frames, and any flat molding. Select Crown Molding for compound cuts where the molding sits at an angle against both the wall and ceiling.
- Set the spring angle (crown mode only). The spring angle is the angle the crown sits against the wall. Most stock crown molding uses 38 degrees. Wider, flatter profiles may use 45 degrees. Check the back of your molding or the manufacturer specs if unsure.
- Read your results. The primary result is the miter angle. In crown mode, the bevel angle also appears. Set both on your compound miter saw before cutting. The complement angle (90 minus the miter) is shown for reference, as some older saws display it that way.
Results update instantly as you type. Use the Share button to send your setup to a helper at the saw, or Copy to paste into a notes app on the job site.
About the Miter Angle Calculator
For a simple miter, the formula is straightforward: each piece takes half the corner angle. A 90-degree corner gets a 45-degree miter on each piece. A 135-degree bay window corner gets a 67.5-degree miter. This applies to baseboards, door and window casings, chair rail, picture frames, and any flat trim.
Crown molding is more complex because the molding is tilted away from both the wall and ceiling at once, requiring a compound cut combining a miter angle and a bevel angle simultaneously. The miter angle uses the formula: arctan(sin(springAngle) x tan(cornerAngle / 2)). The bevel angle uses: arcsin(cos(springAngle) x cos(cornerAngle / 2)). These formulas account for the spring angle, which is the angle the molding sits relative to the wall when installed flat against the ceiling. All calculations run entirely in your browser. No data is stored or transmitted.
Frequently Asked Questions
What miter angle do I use for a standard 90-degree corner?
For a standard 90-degree inside or outside corner, cut each piece at 45 degrees. The two 45-degree cuts join to form the full 90-degree corner. This applies to baseboards, door casings, picture frames, and most other flat trim. If the walls are not perfectly square (common in older homes), measure the actual corner angle with a digital angle finder or a bevel gauge and divide by two for a more accurate cut.
What is the miter angle for a bay window?
A standard bay window forms 135-degree corners where the angled side panels meet the front panel. Each piece of trim at those corners should be cut at 67.5 degrees (135 divided by 2). Some bay windows use 120-degree corners, which require 60-degree miter cuts. Always measure the actual wall angle rather than assuming the standard value, since installation tolerances can vary by a degree or two and affect the fit of the trim.
What is the difference between miter angle and bevel angle?
The miter angle is the left-right rotation of the saw blade, viewed from above. It controls the angle of the cut across the face of the workpiece. The bevel angle is the tilt of the blade from vertical, which angles the cut through the thickness of the workpiece. For flat molding (baseboards, casings), only a miter angle is needed. For crown molding installed at a tilt, both a miter and bevel angle are needed simultaneously, which is why it requires a compound miter saw.
How do I find the spring angle of my crown molding?
Hold the molding against a flat surface with both the top and bottom edges touching (as it would sit against the ceiling and wall). Place a protractor or digital angle gauge against the back face. The angle it reads is the spring angle. Alternatively, check the molding packaging or manufacturer specifications. Most residential crown uses a 38-degree spring angle. Wider profiles with more projection often use 45 degrees. If you cannot determine the angle, test both 38 and 45 on scrap pieces to see which produces the tightest joints.