Angle Cut Calculator
Enter your corner type and dimensions to get the precise miter angle and bevel tilt to set on your saw. Choose from four modes: simple miter for flat trim at any corner, compound miter for crown molding laid flat on the saw bed, polygon frame for multi-sided picture frames or octagons, and unequal-width boards for door casings or mixed-width trim. Results update instantly as you type.
What is a miter angle and when do you need to calculate it?
A miter angle is the amount you rotate your saw table (or tilt the blade) so that the cut face of a board is no longer square to the edge. Two boards each cut at the same miter angle will meet at a corner joint that closes tightly at the face. You calculate a miter angle any time two pieces must meet at a corner other than a flat butt joint: door and window casing, baseboard trim, crown molding, picture frames, octagons, and polygon window surrounds all require precise miter angles. Getting the angle right the first time saves expensive timber and avoids visible gaps.
Simple miter vs. compound miter - which do you need?
A simple miter is a single rotation of the saw table with the blade staying vertical. It handles flat trim, baseboard, door casing, and picture frames - any board that lies flat on the saw bed and meets another board at a corner. A compound miter combines a table rotation (miter angle) and a blade tilt (bevel angle) at the same time. You need a compound miter for crown molding laid flat on the saw bed, angled fascias, and any piece that must fit against two non-parallel surfaces simultaneously. The formulas are different: a simple miter at a 90-degree corner is just 45 degrees each, while a 38-degree-spring crown at the same corner needs a 31.6-degree miter and a 33.9-degree bevel.
Crown molding spring angle - how to find and use it
The spring angle is the angle between the flat back of the crown molding and the wall it sits against. The most common North American profiles are sold as 52/38 stock, meaning the wall angle is 52 degrees and the spring angle (used in saw calculations) is 38 degrees. Wider, flatter profiles often use a 45-degree spring, and some ornate profiles use 30 or 52 degrees. To measure your molding, hold it in a corner formed by two flat surfaces set at 90 degrees and measure the angle at the back of the piece against one surface. Once you know the spring angle, enter the wall corner angle and the spring angle above. The calculator solves the compound geometry and gives you both the miter and bevel settings to dial into your saw.
Practical tips for accurate miter cuts
First, verify your corner angle with an angle finder or protractor before calculating, because room corners vary and are rarely exactly 90 degrees. Second, always make a test cut on scrap wood at the calculated setting and hold the pieces in position before cutting finish material. Third, use a blade with at least 60 teeth for clean miter cuts on painted or veneered stock. Fourth, measure to the long point of the miter when marking pieces for length: the long point is the outside edge of the cut, and it is the reference used for fitting trim in place. Fifth, for crown molding, mark the ceiling and wall contact edges on each piece before you start cutting so you always orient the piece correctly on the saw.
Common polygon miter angles
| Sides | Shape | Miter angle | Interior corner |
|---|---|---|---|
| 3 | Triangle | 60.0° | 60.0° |
| 4 | Square | 45.0° | 90.0° |
| 5 | Pentagon | 36.0° | 108.0° |
| 6 | Hexagon | 30.0° | 120.0° |
| 7 | Heptagon | 25.7° | 128.6° |
| 8 | Octagon | 22.5° | 135.0° |
| 9 | Nonagon | 20.0° | 140.0° |
| 10 | Decagon | 18.0° | 144.0° |
| 12 | Dodecagon | 15.0° | 150.0° |
| 16 | Hexadecagon | 11.25° | 157.5° |
Miter angle to set on the saw for each piece of a regular polygon frame or border. All cuts are identical and the bevel is 0 degrees.
Frequently asked questions
What miter angle do I set for a 90-degree corner?
For a standard 90-degree room corner with flat trim, set both pieces to 45 degrees. Each board carries half the total corner angle. If your corner is slightly out of square, measure the actual angle and enter it above to get the corrected setting.
What are the miter and bevel settings for 38-degree spring crown at a 90-degree corner?
For the most common residential crown (38-degree spring angle at a 90-degree wall corner), set the miter to 31.6 degrees and the bevel to 33.9 degrees. Lay the crown flat on the saw bed with the ceiling edge against the fence. Most compound miter saws have a 31.6-degree detent precisely for this cut.
How do I find the spring angle of my crown molding?
Hold the molding in the corner of two flat surfaces meeting at 90 degrees, just as it would sit in a room. Measure the angle between the back of the molding and the wall surface. Common values are 38 degrees (52/38 profile), 45 degrees (45/45 profile), and 30 degrees for flatter coves. The angle is sometimes printed on the molding packaging or stocked on the label.
How is the polygon miter angle calculated?
For a regular polygon with n equal sides, the miter angle is 180 degrees divided by n. This is also half the exterior angle at each corner. For an octagon (8 sides), the miter is 180 / 8 = 22.5 degrees. All pieces get the same cut. The interior corner angle is (n minus 2) times 180 divided by n.
Why do I get different angles for the two boards in unequal-width mode?
When two boards of different face widths meet at a corner, equal miter angles would produce a joint line that is not straight across the face. The correct cut divides the corner angle unequally, with the narrower board receiving a smaller angle and the wider board a larger one. The formula uses trigonometry to find the exact split so the joint line runs straight across both faces at the corner.
My saw only goes to 50 degrees. What do I do for a steep miter?
If the calculated miter angle exceeds your saw limit (usually 45 to 52 degrees), you can cut the joint as a bevel instead: rotate the board 90 degrees on the saw bed and tilt the blade to the same angle. Alternatively, some carpenters cope one of the two boards rather than mitering both pieces when dealing with angles beyond the saw range.
What is the difference between the miter angle and the cut angle?
Confusion arises because different saw manufacturers label their scales differently. The miter saw setting (also called the saw table angle) is measured from the 0-degree position, which is square to the fence. The cut angle (or cut-off angle) is measured from 90 degrees square, which is 90 minus the saw table setting. For a 45-degree miter, both numbers are the same. For a 30-degree miter, the cut angle is 60 degrees on saws that use that convention. This calculator shows both.