Practical tools for measured work
Miter Angle Calculator
Find the miter saw angle for a regular-shape frame or a custom corner angle.
Sides: whole number ≥ 3. Angle: degrees.
Set your miter saw to the miter angle shown, and cut that same angle on both pieces meeting at the corner.
How it works
How to use it: for a regular shape (a frame, planter or table with equal sides - like a square, hexagon or octagon), choose Regular shape and enter the number of sides. For an irregular corner - an out-of-square wall, an odd-shaped frame - choose Custom corner angle and enter the actual angle between the two pieces.
Formula. Every two-piece corner has an interior corner angle. The miter angle - the number you set on the saw, measured from a square (0°) cut - is half of what's left after the corner angle: miter angle = (180° − corner angle) / 2. For a regular polygon of n equal sides, the corner angle is (n − 2) × 180° / n, so the two modes agree: a 4-sided frame has a 90° corner and a 45° miter; a hexagon has a 120° corner and a 30° miter.
Worked example. With the default (regular shape, 4 sides): corner angle = (4−2) × 180 / 4 = 90°; miter angle = (180 − 90) / 2 = 45° - the familiar 45° setting for a square picture frame. For an 8-sided shape: corner angle = (8−2) × 180 / 8 = 135°; miter angle = (180 − 135) / 2 = 22.5°.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Corner type
- Regular shape (equal sides)
- Number of sides, or corner angle
- 4
Primary result: Miter angle: 45.00 deg.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
This calculates the miter angle for a flat, single-bevel corner joint only - it does not compute compound miter/bevel pairs for angled (non-vertical) material such as crown moulding run at a spring angle, which needs a second, tilt-plane angle as well.
"Regular shape" mode assumes every side is the same length and every corner is identical, which is true for a regular polygon but not for an arbitrary irregular frame - measure each corner separately with the custom-angle mode if your shape isn't regular.
Frequently asked questions
Why does a square frame need a 45° miter, not a 90° cut?
The 90° is the corner angle the two boards form once joined - each board only needs to turn half of that (45°) so the two 45° cuts add up to the full 90° corner.
What if my wall or frame corner isn't a standard shape?
Measure the actual angle between the two surfaces with a protractor or angle finder, then use Custom corner angle mode with that measurement instead of guessing a side count.
Does this account for saw blade kerf or material thickness?
No - it returns the geometric angle only. Kerf and thickness affect the piece lengths you cut to, not the angle, and depend on your specific saw and material.
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