Calculators/Compound miter

Compound miter calculator for crown

Miter and bevel settings for sprung moulding cut flat on the table — at any spring angle and any corner, not just 38° into a square corner.

The moulding

The angle between the wall and the back of the moulding when installed.

Saw settings

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Check the result against the job. This does the arithmetic from the values you enter. Building codes, span tables and material specifications vary by jurisdiction and by product, and the governing document is your approved drawings and your local code. Nothing you type here leaves your browser: the calculation runs on your device and we never receive it.

How this is checked. Every formula on this site runs from one shared calculation engine, and every one has a test fixture whose expected answer was worked out from the geometry or taken from a figure the trade already publishes — never from what the code returns. Some land exactly, which is the point: a 6/12 hip over a 144″ run is exactly 216″, a 45° crown in a square corner bevels at exactly 30°, and a 30° conduit bend has a multiplier of exactly 2. Where a number is a convention rather than arithmetic — a code limit, a waste allowance, bundles per square — it is an input with a stated default rather than a hidden constant. Found something wrong? Tell us at [email protected] and we will fix it and say so.

Flat on the table, not nested

These settings are for cutting the moulding lying flat on the saw table. The alternative — nesting it against the fence at its installed angle and cutting a simple 45 — needs no compound settings at all, but it only works for moulding narrow enough to fit under the saw, and only for square corners.

Flat cutting is what you need for wide crown, for shallow saws, and for any corner that is not 90°. It is also what most published crown charts assume.

Where the numbers come from

Two things combine. The moulding sits tipped away from the wall at its spring angle, and the walls meet at some corner angle. Flattening the moulding onto the table converts that tip into both a miter and a bevel, which is why one cut needs two settings.

The corner matters through the turn, not directly. A run of moulding turns through 180° minus the corner, and each piece takes half of that. A square corner turns 90°, so each piece is 45° in plan. A 135° octagon corner turns only 45°, so each piece is 22.5° — and every setting comes down accordingly.

Two checks worth the ninety seconds. Measure the corner rather than assuming 90; framed corners are routinely a degree or two out and it shows on crown. And cut a test pair in scrap before the real material — an inside and an outside corner use the same settings, but the offcut you keep is the opposite one, and that is an easy way to lose a length of expensive moulding.

Common questions

What are the saw settings for 38 degree crown molding?

Cut flat on the table in a square corner, a 38 degree crown takes a miter of 31.6 degrees and a bevel of 33.9 degrees. A 45 degree crown in a square corner takes 35.3 miter and exactly 30 bevel.

What is the spring angle of crown molding?

The angle between the wall and the back of the moulding when it is installed. The two common profiles are 38 and 45 degrees. You can measure it by setting the moulding into a corner formed by a square and reading the angle, or by checking the two flats on the back.

Do the angles change for a corner that is not square?

Yes, and not in proportion. The moulding turns through 180 degrees minus the corner angle, so a 135 degree octagon corner turns through only 45 and needs a much smaller miter — about 14.3 degrees at a 38 degree spring, against 31.6 for a square corner.

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