Miter Angle Calculator
Miter Angle
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Corner Angle
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Table Saw Blade Angle
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How Miter Angles Work
A miter angle is the angle at which two pieces of material are cut so they meet to form a joint at a specific corner angle. Miter joints are fundamental in woodworking, picture framing, crown molding, baseboard trim, and any project requiring angled corners. According to the WOOD Magazine and Fine Woodworking, accurate miter cuts are one of the most common yet precision-demanding tasks in the workshop.
For regular polygons (shapes where all sides and angles are equal), the miter angle is always half the interior angle. The interior angle of any regular polygon is calculated as (n - 2) x 180 / n, where n is the number of sides. This calculator computes the miter angle, the corner (interior) angle, and the table saw blade angle automatically. You can also enter a custom corner angle for irregular joints.
Whether you are building a hexagonal planter, framing a picture, installing crown molding, or constructing an octagonal gazebo, this calculator eliminates the guesswork and math errors that lead to gapped joints and wasted material.
The Miter Angle Formula
The miter angle formula is derived from basic polygon geometry. For a regular polygon with n sides:
Interior Angle = (n - 2) x 180 / n
Miter Angle = Interior Angle / 2
Table Saw Blade Angle = 90 - Miter Angle
- n — number of sides in the polygon
- Miter Angle — the angle to set on your miter saw or miter gauge
- Blade Angle — the tilt angle for a table saw blade (measured from perpendicular to the fence)
Worked example: For an octagon (8 sides): Interior angle = (8 - 2) x 180 / 8 = 135 degrees. Miter angle = 135 / 2 = 67.5 degrees. Table saw blade angle = 90 - 67.5 = 22.5 degrees.
Key Terms You Should Know
- Miter Joint — a joint made by cutting two pieces at angles so they meet to form a corner. Each piece is cut at the miter angle.
- Bevel Angle — the angle of a cut through the thickness of the wood (vertical tilt). Combined with a miter angle, this creates a compound miter for tilted joints.
- Compound Miter — a cut requiring both a miter angle (horizontal rotation) and a bevel angle (vertical tilt), commonly needed for crown molding and angled picture frames.
- Kerf — the width of material removed by the saw blade. Standard kerf is about 1/8 inch (3.2 mm) and must be accounted for when measuring cuts.
- Fence Angle — on a table saw, the blade angle is measured from the fence or table surface, which is 90 degrees minus the miter angle.
Miter Angles for Common Polygons
The following reference table shows the miter angle and saw settings for the most commonly built polygon shapes in woodworking and construction. These angles are exact for regular (equal-sided) polygons.
| Shape | Sides | Interior Angle | Miter Angle | Blade Angle |
|---|---|---|---|---|
| Triangle | 3 | 60.0 | 30.0 | 60.0 |
| Square / Rectangle | 4 | 90.0 | 45.0 | 45.0 |
| Pentagon | 5 | 108.0 | 54.0 | 36.0 |
| Hexagon | 6 | 120.0 | 60.0 | 30.0 |
| Octagon | 8 | 135.0 | 67.5 | 22.5 |
| Decagon | 10 | 144.0 | 72.0 | 18.0 |
| Dodecagon | 12 | 150.0 | 75.0 | 15.0 |
Practical Examples
Example 1 — Picture frame: A rectangular picture frame has 4 corners at 90 degrees each. Miter angle = 90 / 2 = 45 degrees. Set your miter saw to 45 degrees. Cut each piece of molding with a 45-degree angle at both ends, one left and one right. Use our diagonal calculator to verify frame squareness by measuring corner-to-corner.
Example 2 — Hexagonal planter: A hexagon has 6 sides with interior angles of 120 degrees. Miter angle = 60 degrees. Set your miter saw to 60 degrees (or table saw blade to 30 degrees). Cut 6 equal-length boards with opposing 60-degree miters at each end. Apply wood glue and clamp using a band clamp for even pressure.
Example 3 — Non-standard corner: A bay window creates a 135-degree corner. Miter angle = 135 / 2 = 67.5 degrees. For baseboard trim, set the miter saw to 67.5 degrees. If your saw only goes to 60 degrees, use the "custom corner angle" field in this calculator to compute an alternative cutting approach.
Tips for Perfect Miter Joints
- Use a digital angle gauge: Even quality miter saws can be off by 0.5-1 degree. A $20 digital gauge verifies your setting and eliminates cumulative errors across multiple joints.
- Make test cuts on scrap: Always cut two test pieces at your calculated angle and check the fit before cutting final material. Adjust by 0.25 degrees if needed.
- Account for blade kerf: The saw blade removes approximately 1/8 inch of material. Measure from the waste side of the cut line to maintain correct piece length.
- Ensure boards are flat and square: Twisted or cupped boards produce gapped joints regardless of angle accuracy. Joint and plane boards first if needed.
- Use splines or biscuits: Miter joints have minimal long-grain glue surface. Adding splines, biscuits, or dowels dramatically increases joint strength.
Frequently Asked Questions
What miter angle do I need for a picture frame?
A standard picture frame requires a 45-degree miter angle. This is because a rectangle has 90-degree interior corners, and each piece of the joint contributes half: 90 / 2 = 45 degrees. Set your miter saw to exactly 45 degrees. To verify accuracy, cut two test pieces and check that they form a perfect 90-degree corner with no gap. For non-rectangular frames (trapezoids, diamonds), calculate the interior angle at each corner and divide by 2 to get the miter angle for that specific joint.
What is the miter angle for a hexagon?
A regular hexagon has interior angles of 120 degrees, so the miter angle is 120 / 2 = 60 degrees. On a miter saw, set the angle to 60 degrees. On a table saw, set the blade angle to 90 - 60 = 30 degrees from the fence. Hexagonal projects like planters, shelves, and picture frames require 6 boards of equal length, each with opposing 60-degree miter cuts. Use a band clamp or strap clamp during glue-up to apply even pressure to all 6 joints simultaneously.
Why do my miter joints have gaps?
Gapped miter joints typically result from one of four causes: inaccurate saw angle (even 0.5 degrees off accumulates across multiple joints), blade wobble or deflection, boards that are not flat or straight, or inconsistent piece lengths. To troubleshoot, first verify your saw angle with a digital angle gauge. Then check that your wood is flat by placing it on a known-flat surface. Make test cuts on scrap wood and dry-fit before cutting final pieces. For slight gaps, you can use a block plane to shave the joint face or fill with a wood glue and sawdust mixture.
What is a compound miter angle?
A compound miter combines a miter angle (horizontal rotation of the saw head) with a bevel angle (vertical tilt of the saw blade) to create joints where pieces meet at a corner angle AND tilt away from vertical. Crown molding is the most common application: the molding sits at an angle between the wall and ceiling, requiring both miter and bevel settings. Compound miter calculations involve trigonometry and are more complex than simple miters. Use our crown molding calculator for these specialized cuts.
How do I calculate miter angles for non-regular shapes?
For non-regular polygons or custom corner angles, the miter angle is simply half of the desired corner angle. Measure the actual corner angle with a digital protractor or angle finder tool. Enter that angle in the "Custom Corner Angle" field of this calculator. For example, a bay window with a 135-degree corner needs a miter angle of 67.5 degrees. Walls rarely meet at exactly 90 degrees in older homes, so always measure the actual corner rather than assuming 90 degrees. A difference of 1-2 degrees is common and visible in the finished joint.