Get the exact miter angle for any project. Choose an equal-sided frame or box (like a picture frame, hexagon, or octagon), or enter a custom inside corner angle and we'll tell you the miter to set on your saw.
To build a flat frame or box with N equal sides, cut each end at a miter angle of 180 ÷ N degrees — so a 4-sided frame = 45°, a 6-sided hexagon = 30°, an 8-sided octagon = 22.5°. For two pieces meeting at any inside corner angle A, the miter for each piece is (180 − A) ÷ 2 — a standard 90° corner = 45°. Crown molding needs a compound (miter + bevel) cut; see the spring-angle chart below. Use the calculator to get exact angles.
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For any flat (single-plane) equal-sided frame or box, the miter angle for each cut is 180 ÷ number of sides, and the interior corners are (N − 2) × 180 ÷ N. Here are the most common shapes.
| Sides | Shape | Miter Angle (each cut) |
Interior Angle (at corner) |
|---|---|---|---|
| 3 | Triangle | 60° | 60° |
| 4 | Square / Rectangle | 45° | 90° |
| 5 | Pentagon | 36° | 108° |
| 6 | Hexagon | 30° | 120° |
| 7 | Heptagon | 25.7° | 128.6° |
| 8 | Octagon | 22.5° | 135° |
| 9 | Nonagon | 20° | 140° |
| 10 | Decagon | 18° | 144° |
| 12 | Dodecagon | 15° | 150° |
The miter angle is what you set on the saw (the angle off of a square 0° cut). Set your saw to the miter angle and cut both ends of each piece, mirroring the cut so the angled faces meet.
A miter joint is just two pieces of stock whose ends are cut at an angle so they meet to form a corner. The total turn around a closed flat shape is always 360°, and that turn is shared evenly across all the corners. Each corner is formed by two cuts (one on each piece), so each individual cut takes half of the turn at that corner.
That is where the formula comes from. For an equal-sided shape with N sides, the turn at each corner is 360 ÷ N, and each of the two cuts handles half of that: (360 ÷ N) ÷ 2 = 180 ÷ N. So a 4-sided frame is 180 ÷ 4 = 45°, a hexagon is 30°, and an octagon is 22.5°.
Frame / box: miter = 180 ÷ N
Any corner: miter = (180 − A) ÷ 2
For a single corner where you already know the inside angle A (not a full closed shape), the two pieces together have to fill that angle, so each is cut at (180 − A) ÷ 2. A standard square corner of 90° gives (180 − 90) ÷ 2 = 45°, and a wide 135° corner (like an octagon's) gives (180 − 135) ÷ 2 = 22.5°. The miter angle is always the setting off of a straight, square cut, which is how miter saws are marked.
Crown molding does not lie flat against the wall — it tips out at the top at an angle called the spring angle (most commonly 38° or 45°, often stamped on the back of the molding). Because the molding sits at an angle, a corner needs a compound cut: the saw is both mitered (table rotated) and beveled (head tilted) at the same time.
If you cut crown flat on the saw table (face up), use these compound settings for a standard 90° corner:
| Spring Angle | Miter Setting | Bevel Setting |
|---|---|---|
| 38° spring | 31.6° | 33.9° |
| 45° spring | 35.3° | 30° |
Values are for a 90° corner cutting crown lying flat on the table. These are the standard, widely used settings — the 38°/45° spring angle is the angle between the back of the molding and the wall.
Flat vs. nested cutting. The simpler alternative is to cut crown nested — held upside down against the saw fence at its actual spring angle, with the ceiling edge on the table and the wall edge against the fence. Cut that way, the molding only needs a simple 45° miter (no bevel) for a 90° corner, just like a flat frame. Nested cutting is easier to set up but limited by how tall a piece your saw can hold against the fence; flat (compound) cutting handles wider crown but requires getting both the miter and bevel exactly right.
The miter angle is the same for an inside corner and an outside corner of the same shape — what changes is the direction of the cut and which side of the piece keeps the long point.
A sliding compound miter saw cuts both miter and bevel, so it handles flat frames and crown molding compound angles alike. The single most useful tool for mitered work.
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For a 6-sided frame (a hexagon), cut each end at a 30° miter angle. The rule for any flat equal-sided frame or box is miter angle = 180 ÷ number of sides. With 6 sides, 180 ÷ 6 = 30°, and the six pieces meet at interior corner angles of 120°. Set your miter saw to 30° and cut both ends of each piece, mirroring the cut so the angles point the right way.
For an equal-sided frame or box with N sides, the miter angle for each cut is 180 ÷ N. A 4-sided frame is 180/4 = 45°, a 6-sided hexagon is 30°, and an 8-sided octagon is 22.5°. For two pieces meeting at any inside corner of A degrees, the miter for each piece is (180 − A) ÷ 2. A standard 90° corner gives (180 − 90)/2 = 45°. The miter saw setting is the angle off of a square (0°) cut.
The miter angle for a standard 90° corner is 45° per piece. The formula is miter = (180 − the inside corner angle) ÷ 2, so (180 − 90)/2 = 45°. Each of the two pieces is cut at 45° and together they form the square 90° corner. This is the most common miter cut, used for picture frames, door casing, and box corners.
Crown molding sits at an angle to the wall (the spring angle) so it needs a compound cut, not a single miter. For a standard 90° corner: with a 38° spring angle, set the miter to 31.6° and the bevel to 33.9°; with a 45° spring angle, set the miter to 35.3° and the bevel to 30°. Alternatively you can cut crown nested (held upside down against the fence at its spring angle) and use a simple 45° miter. Always check the spring angle stamped on the molding or measure it.
A miter cut swings the saw blade left or right across the face of the board (you rotate the saw table), while a bevel cut tilts the blade so the cut is angled through the thickness of the board (you tip the saw head over). A simple frame corner needs only a miter. Crown molding and other parts that sit at an angle need both at once, which is called a compound cut — and that is why a compound miter saw exists.