Miter Angle Calculator

How to Use the Miter Angle Calculator

Enter the number of sides of the regular polygon you want to build. The calculator instantly returns three numbers: the interior angle at each corner, the miter angle you should set on your saw, and the full corner turn angle. A square frame has four sides, so you set your miter saw to 45°. A hexagonal tabletop has six sides, which means a 30° miter. For any regular polygon, the miter angle is simply 180 divided by the number of sides.

Cut each end of every piece at the calculated miter angle, making sure matching pieces are identical in length measured between the long points. Dry-fit the assembly before gluing to confirm the joints close cleanly. A test cut on scrap stock is cheap insurance against a ruined workpiece.

What Is a Miter Angle

A miter angle is the angle a saw blade cuts across the face of a board so that two pieces meet to form a corner. Each of the two cuts removes half of the total corner turn, so the two pieces share the work. For a closed polygon, the exterior angles sum to 360°. Dividing that by the number of corners gives the angle the walk around each corner, and half of that is the miter angle. For a square, 360 ÷ 4 = 90°, and half is 45°. For an octagon, 360 ÷ 8 = 45°, and half is 22.5°.

Common Polygon Miter Angles

Use this quick reference for common regular polygon shapes used in woodworking:

• 3 sides (equilateral triangle): 60° miter
• 4 sides (square): 45° miter
• 5 sides (pentagon): 36° miter
• 6 sides (hexagon): 30° miter
• 8 sides (octagon): 22.5° miter
• 12 sides (dodecagon): 15° miter

Miter vs Bevel Angles

A miter cut changes the direction of a board in the horizontal plane, like the corners of a picture frame. A bevel cut angles the blade through the thickness of the board, producing a sloped edge. A compound miter combines both at once, which is how you cut crown moulding or the tapered sides of a planter box. This calculator solves the flat miter case for a regular polygon. For compound angles, you must also account for the tilt of the sides relative to vertical.

Frequently Asked Questions

What is a miter angle?

A miter angle is the angle cut on the end of a board so two pieces join cleanly at a corner. For a regular polygon with N sides, the miter angle equals 180 ÷ N degrees.

How do I calculate a miter angle for a picture frame?

A square or rectangular picture frame has four 90° corners. Each joining piece is cut at 45°, which is half of the corner turn.

What's the difference between miter and bevel?

A miter is an angled cut across the face of a board. A bevel is an angled cut through the thickness, tilting the blade. Miters are for corners, bevels are for sloped edges.

How do I cut a hexagonal frame?

A hexagon has six sides, so each miter angle is 180 ÷ 6 = 30°. Cut all twelve ends at 30° and join six equal-length pieces.

Why don't my corners close perfectly?

Tight miters depend on accurate saw angles and equal piece lengths. Check your saw gauge, use a sharp blade, and measure consistently from the same reference edge.