Miter Angle Calculator
Miter saw settings for picture frames and polygons, trim at any corner angle, and crown molding miter and bevel for 38, 45 or 52 degree spring angles.
The interactive tool loads here when JavaScript runs.
About this toolWhat is the Miter Angle Calculator?
Most miter cuts reduce to halving an angle: two pieces meeting at a corner each take half of what is missing from a straight line. The confusion comes from crown molding, which leans out from the wall at its spring angle, so a cut made with the molding flat on the saw table needs a compound angle, a miter and a bevel together. This calculator gives the saw settings for all three jobs.
In polygon mode, enter the number of sides for a frame, planter or table apron and read the miter for each end, the interior angle and the inside edge length from your stock width. In corner mode, enter any corner angle for baseboard, casing or a bay window. In crown mode, enter the wall angle and the spring angle (38° for 52/38 crown, 45° for 45/45) to get the flat-on-table miter and bevel and the nested setting.
Angles can be shown on the miter saw scale, where 0 is a square cut, or as a protractor reading where 90 is square, because the two conventions trip up many first cuts.
- Polygon miters with interior angle and inside edge length
- Flat trim miter for any corner angle
- Crown compound miter and bevel for 38°, 45°, 52° or any spring angle
- Nested crown setting and a chart for common wall angles
- Miter saw or protractor scale; copy and share link
How to use the Miter Angle Calculator
- Choose crown molding, trim at a corner, or polygon frame.
- For crown, enter the wall corner angle and pick the spring angle; add the width across the back if you want the layout line.
- For trim, enter the angle between the two pieces; for a polygon, enter the number of sides and optionally the outside length and stock width.
- Pick whether to show angles on the miter saw scale or a protractor scale.
- Read the settings, make a test cut on scrap, then copy the result for the job.
Worked examples
52/38 crown in a square corner
Input
Crown, wall 90°, spring 38°
Output
Miter 31.62°, bevel 33.86°; nested miter 45°
Most miter saws have detents at 31.6° and 33.9° for exactly this cut.
Crown around a 135° bay window corner
Input
Crown, wall 135°, spring 38°
Output
Miter 14.31°, bevel 17.55°
The wider the corner, the smaller both angles get. With 45/45 crown the same corner needs 16.32° and 15.70°.
Hexagon frame from 2 in stock
Input
Polygon, 6 sides, outside edge 12 in, stock 2 in wide
Output
Miter 30°, interior angle 120°, inside edge 9-11/16 in
The inside edge is the outside length minus 2 x 2 x tan(30°), useful for marking short points.
Background and insight
A regular polygon with n sides turns 360 degrees in n corners, so each corner turns 360 / n and each of the two pieces at that corner takes half: 180 / n. Four sides give 45°, six give 30°, eight give 22.5°. For flat trim at a corner of A degrees, each piece is cut at (180 - A) / 2 on the saw scale, so 45° at a square corner and 22.5° at a 135° bay window corner.
For crown molding laid flat, with spring angle S measured between the back of the molding and the wall and wall angle A, the settings are miter = atan(sin S / tan(A/2)) and bevel = asin(cos S x cos(A/2)). For 52/38 crown in a 90° corner that gives 31.62° and 33.86°, and for 45/45 crown 35.26° and 30.00°, the same figures printed in miter saw manuals such as Ridgid's crown molding chart. Cutting nested (upside down, leaning against the fence at its spring angle) needs only the plain miter of (180 - A) / 2.
Common use cases
Installing crown molding
Get the compound settings for inside and outside corners at any wall angle and spring angle.
Picture frames and boxes
Set the saw for square, hexagonal or octagonal frames and find the inside edge length.
Baseboard and casing at odd corners
Halve a measured corner angle for trim around bay windows and angled walls.
Converting between saw scales
Turn a miter saw setting into a protractor or miter gauge reading and back.
Tips and limitations
- Measure odd corners with a sliding bevel or digital angle finder, then halve the reading rather than trusting 90°.
- Outside corners use the same numbers as inside corners; only the side of the blade you cut on changes.
- Check your crown's spring angle by holding it against a framing square; not every profile is 38° or 45°.
- Coping inside corners hides small wall errors better than a mitered joint.
- Table saw miter gauges often read 90° at a square cut. Switch the scale before you set the gauge.
Frequently asked questions
What angle do I cut crown molding for a 90 degree corner?
For 52/38 crown cut flat on the saw: miter 31.62° and bevel 33.86°. For 45/45 crown: miter 35.26° and bevel 30°. Cut nested upside down against the fence, both types need a plain 45° miter and no bevel.
How do you calculate a miter angle for a polygon?
Divide 180 by the number of sides. A hexagon needs 30° on each end, an octagon 22.5° and a pentagon 36°. Each corner of the frame is made from two pieces that together turn 360 / n degrees.
What is the miter angle for a 135 degree corner?
For flat trim like baseboard, set the saw to (180 - 135) / 2 = 22.5° on each piece. For 52/38 crown cut flat, use 14.31° miter and 17.55° bevel.
What is a crown molding spring angle?
The angle the molding makes with the wall once installed. 52/38 crown sits at 38° from the wall and 52° from the ceiling; 45/45 crown sits at 45° to both. The calculator uses the angle to the wall.
Why does my miter saw say 45 when the protractor says 90?
Saws and gauges use different zero points. A miter saw reads 0 for a square cut and 45 for a frame corner; many protractors and table saw gauges read 90 for a square cut, so the same cut is 45 on one and 45 or 135 on the other depending on the side.
Do outside corners use different angles than inside corners?
The numbers are the same for the same corner angle. What changes is which piece goes on which side of the blade and which end is kept, so mark the waste side before you cut.
Is there an in-depth guide to the Miter Angle Calculator?
Yes. “Crown Molding Angles and Miter Math: From 180/n to Compound Cuts” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
Related Tools You May Like
Free, in-browser tools that pair well with this one.