Crown Molding Angle Calculator

The exact miter and bevel to set on your saw for any crown molding corner. Choose how you cut it, your spring angle, and the real corner angle — including out-of-square, vaulted, octagon and bay-window corners that a 90°-only chart gets wrong.

Cut method
Spring angle (angle off the wall)
Corner type
The angle between the two walls, measured with a digital angle finder or a bevel gauge. A normal square corner is 90°. Out-of-square walls are often 87–93°.

Angles are computed with standard compound-angle geometry for a sprung molding. Real walls are rarely perfectly square or flat — always cut a scrap test piece and dry-fit before cutting your finished molding.

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Building frames, boxes or polygon shapes instead? The Miter Angle Calculator handles flat picture frames, any-sided polygons, and splayed boxes (planters, hoppers, staved columns) — the same compound-angle math, set up for projects that don’t touch a wall.

Reading your two saw settings

A compound miter saw has two independent adjustments, and crown molding usually needs both:

The settings depend on three things: your molding’s spring angle, the corner angle of the wall, and which method you use to hold the molding while cutting.

Spring angle: the number that changes everything

The spring angle is the angle between the flat back of the molding and the wall once it’s installed. Stock molding is almost always one of two profiles — 38° (labelled 52/38) or 45° (labelled 45/45) — and the figure is often stamped on the back edge. Using 38° settings on a 45° molding (or the reverse) opens gaps that you cannot sand away, so confirm it before you cut. If you’re unsure, stand an offcut in its installed position against a framing square and read the angle off the wall side with a protractor or digital angle finder.

The two cutting methods

Nested (upright): the molding sits upside-down against the fence, tilted at its spring angle, the way it will hang on the wall. Because the spring angle is already “built in” by that position, you only set a miter — bevel stays at zero. It’s the simplest to remember (a 90° corner is just 45°), but you must hold the piece at exactly the spring angle every cut, which usually means a stop block or crown jig, and the molding has to fit within the saw’s height capacity.

Flat on the table: the molding lies flat, face up. Now the saw has to recreate the spring angle itself, so you set both a miter and a bevel — a true compound cut. The payoff is that the piece is fully supported and the cuts are repeatable, and you can cut wide molding that would never fit nested. This is the method most calculators give numbers for.

Inside vs outside corners

The angles are the same for an inside and an outside corner of the same opening; what changes is orientation — which side of the cut becomes the long point, and which way you swing the saw. On an inside corner the visible face is the short side of the cut; on an outside corner it’s the long side. The calculator spells out the left-piece and right-piece setup for whichever you pick. For inside corners, many trim carpenters skip the miter entirely and cope the joint instead — see the FAQ.

The math (for the curious)

For the flat-on-table method, with spring angle S measured off the wall and corner angle C between the two walls:

miter  = arctan( sin S ÷ tan(C ÷ 2) )
bevel  = arcsin( cos S × cos(C ÷ 2) )

The bevel term uses cos(C÷2). A lot of online calculators use sin(C÷2), which happens to give the right answer at exactly 90° but drifts off as soon as the corner isn’t square — so they quietly fail on octagons, bay windows and vaulted ceilings. This one uses the correct form, which is why the octagon and hexagon rows below come out right. For the nested method the spring angle is handled by the molding’s position, so the miter is simply (180° − C) ÷ 2 with no bevel.

Standard angle chart (flat-on-table, inside corner)

CornerSpringMiterBevel
90° (square)38° (52/38)31.6°33.9°
90° (square)45° (45/45)35.3°30.0°
90° (square)52° (38/52)38.2°25.8°
135° (octagon)38° (52/38)14.3°17.6°
135° (octagon)45° (45/45)16.3°15.7°
120° (hexagon)38° (52/38)19.6°23.2°
120° (hexagon)45° (45/45)22.2°20.7°

For a nested cut, the miter on a 90° corner is 45°, on a 135° octagon corner it’s 22.5°, and on a 120° hexagon corner it’s 30° — with the bevel always at zero. Enter your own numbers above for anything in between.

Before you cut the good stuff

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Frequently asked questions

What miter and bevel angle do I set for crown molding on a 90° corner?

It depends on the spring angle and how you cut it. Flat on the saw table (compound cut), 90° corner: a 38° spring (52/38) needs 31.6° miter and 33.9° bevel; a 45° spring needs 35.3° miter and 30.0° bevel; a 52° spring needs 38.2° miter and 25.8° bevel. Cutting nested (upright against the fence at the spring angle), a 90° corner is a simple 45° miter with zero bevel.

What is the spring angle and how do I find mine?

It’s the angle between the molding’s flat back and the wall when installed. The two common profiles are 38° (labelled 52/38) and 45° (45/45), usually stamped on the back edge. To measure it, set an offcut in its installed position with its two flat back faces against a square — one on the wall side, one on the ceiling side — and read the angle off the wall with a protractor or digital angle finder.

Should I cut crown molding flat or nested?

Both work. Nested uses a simple miter and no bevel, but you have to hold the piece at exactly the spring angle every time (usually with a stop or jig), and the molding has to fit the saw’s capacity. Flat-on-table uses a compound miter and bevel; the piece is fully supported so cuts repeat cleanly, and it handles wide molding a nested cut can’t. This calculator gives both — switch the cut method at the top.

How do I cut crown molding for a corner that isn’t 90 degrees?

Measure the actual corner with a digital angle finder or a bevel gauge and protractor, then type it in. Octagon corners are about 135°, hexagon about 120°, and out-of-square walls are often 87–93°. The bevel changes with the corner angle, so a 90°-only chart will be wrong on a bay window or vaulted ceiling. Cut a scrap test piece and dry-fit before committing.

Why do my inside corners gap even with the right angles?

Usually the corner isn’t truly 90°, the molding wasn’t held at a consistent spring angle, or the wall faces aren’t flat. Many trim carpenters cope inside corners instead of mitering: cut the first piece square into the corner, then cope the profile of the second piece to nest against it. Coped joints absorb out-of-square walls far better, which is why mitering is mostly kept for outside corners.