Miter Angle Calculator

The miter angle calculator divides the corner angle between two walls by two, giving the saw setting for each piece of flat trim. This is for flat trim, which has no spring angle. A standard 90° corner needs 45° cuts, and a 135° bay window corner needs 67.5° cuts.

Last reviewed September 2026Method & sources Report an error

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Miter Saw Angle

45.00 °

Breakdown
Miter Saw Angle	45.00°

How to Calculate Miter Angle

Two trim pieces meeting at a corner each get cut at half the angle formed between the two walls. The two cuts add up to the full corner angle when joined. A standard square corner (90°) splits into two 45° miters, while a wider corner (like a 135° bay window angle) splits into two 67.5° miters. This applies to flat trim cut on the flat (baseboard, door/window casing, chair rail cut without a spring angle). Crown molding cut against a tilted fence needs a compound angle, both a miter and a bevel. That is a different, more involved calculation, and this calculator covers only the miter portion of it.

Example: Standard square corner (90° between the two walls)

A standard square corner (90° between the two walls): Miter angle: 90 ÷ 2 = 45° Each piece of trim gets cut at 45° on the miter saw. That is the most common trim corner setting. For a 135° bay window corner instead: 135 ÷ 2 = 67.5° per piece.

What Is Miter Angle?

A miter angle calculator converts a corner's wall angle into the saw angle setting needed to cut flat trim (baseboard, casing, chair rail) so the two pieces meet cleanly. Most corners are a standard 90°, needing the very common 45° miter setting. An out-of-square or non-rectangular corner (a bay window, an angled wall) needs a different setting entirely.

Miter Angle: Pros and Cons

Pros

Works for any corner angle, not only the standard 90° square corner most trim calculators assume
Simple, direct formula with no ambiguity for flat trim cut without a spring angle
Useful for an out-of-square room or an angled wall, where a plain 45° miter won't actually close the gap

Cons

Covers flat trim only (baseboard, casing, chair rail cut flat). Crown molding cut against a tilted saw fence needs a compound miter and bevel angle together, a different and more involved calculation
Doesn't measure your actual corner angle for you. An out-of-square corner should be measured directly (with a protractor or angle finder) rather than assumed to be exactly 90°, since most real-world corners are at least slightly off
A single miter angle assumes both pieces meeting at the corner are cut at the same angle. Some designs intentionally use an uneven split, which this calculator doesn't account for

Miter Angle: What a Pro Checks

Measure your actual corner with a protractor or angle finder before cutting. Most real corners aren't exactly 90°, and this calculator's advantage over a fixed 45° assumption only pays off if you use the real angle.
This covers flat trim only. Crown molding cut against a tilted fence needs a compound miter and bevel together, not this miter-only result.
The same half-angle formula applies to an inside or an outside corner. Only the direction the trim faces and how you orient it on the saw changes, not the angle itself.

Frequently Asked Questions

What angle do you cut baseboard for a corner?

For a standard 90° square corner, cut each piece at a 45° miter. The two 45° cuts add up to the full 90° corner when joined.

How do you calculate miter angle for an odd corner?

Measure the actual angle between the two walls, then divide by 2. A 135° corner (common on a bay window) needs a 67.5° miter on each piece, not the standard 45°.

Does crown molding use the same miter angle as baseboard?

Not exactly the same setup. Crown molding installed against a tilted saw fence (the common method) needs both a miter angle and a bevel angle together, a compound cut, because of the molding's spring angle. This calculator gives the miter portion for flat trim. Crown molding needs an additional bevel setting from a compound-angle reference chart specific to your molding's spring angle.

Why doesn't my 45° miter close the gap at a corner?

Most likely because the actual corner isn't exactly 90°. Real walls are often slightly out of square. Measure the actual angle with a protractor or angle finder and use this calculator's formula (angle ÷ 2) for the correct miter setting instead of assuming a standard 45°.

What is the miter angle for an outside corner vs. an inside corner?

The same formula applies to both (half the corner angle). The difference between inside and outside corners is which direction the trim faces and how the miter saw is oriented for the cut, not the angle value itself.

Carpentry & Trim