What are the miter and bevel for crown molding on a square corner?

For the common 52/38 crown (38° spring angle) cut flat on a compound saw: miter 31.6°, bevel 33.9°. For 45/45 crown: miter 35.3°, bevel 30°. Most compound miter saws have detents at exactly these numbers. Nested upside down against the fence instead, a square corner is a plain 45° miter with no bevel.

How do I find the spring angle of my crown?

Sit a piece in a framing square the way it sits on the wall and ceiling, and measure how far it reaches along each leg: the drop down the wall and the projection across the ceiling. The spring angle is the arctangent of projection ÷ drop. Equal numbers mean 45°; a drop about 1.28 times the projection means 38°.

My corner is not 90°. What changes?

Both angles. Measure the corner with an angle finder, type it in, and the calculator works the compound cut for that corner. A 135° corner on 38° crown is a 14.3° miter and a 17.6° bevel — much gentler than a square corner. Nested, it is a 22.5° miter.

Which edge is the long point?

On an inside corner the bottom edge (the one against the wall) is the long point; on an outside corner the top edge (against the ceiling) is. Cut a test pair from offcuts and hold them in the corner before you cut the real length.

Crown molding calculator

Corner angle

The angle between the two walls — 90 for a square corner, inside or outside. Measure it; old houses lie.

Spring angle

38 for 52/38 crown, 45 for 45/45. Or fill the two measurements below.

Drop on the wall (optional)

Projection on the ceiling (optional)

Any unit, as long as both match — only their ratio is used.

— miter

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Geometry on the angles you type. Walls and ceilings are rarely perfect: the test pair tells you what the numbers cannot, and a half-degree tweak is normal.

Crown sits at an angle between the wall and the ceiling, so a corner needs a compound cut — a miter and a bevel together — when the piece lies flat on the saw table. Type the corner and the crown's spring angle and read both. The nested setting (crown upside down, leaning against the fence at its spring angle) needs only a plain miter, and is shown too.

Worked example

A living room with a slightly open corner measured at 92°, and 52/38 crown. The half-corner is 46°. Miter = atan(sin 38° ÷ tan 46°) = atan(0.616 ÷ 1.036) = 30.7°. Bevel = asin(cos 38° × cos 46°) = asin(0.788 × 0.695) = 33.2°. Nested, it is a (180 − 92) ÷ 2 = 44° miter. A square-corner setting would leave a gap you could slide a pencil into.

Try one

Quick referencefor crown

Square corner, flat: 38° spring: miter 31.6°, bevel 33.9° · 45° spring: miter 35.3°, bevel 30.0° · 52° spring: miter 38.2°, bevel 25.8°
Nested: miter = (180 − corner) ÷ 2, no bevel · 90° corner = 45° · 135° = 22.5°
Spring angle: atan(projection ÷ drop) · equal = 45° · drop ≈ 1.28 × projection = 38°
Long point: inside corner: bottom (wall) edge · outside corner: top (ceiling) edge

The formula

miter = atan(sin spring ÷ tan(corner ÷ 2)) · bevel = asin(cos spring × cos(corner ÷ 2))

The angles are the saw's own readings from square — the numbers on its miter and bevel scales. On a square corner they come out to the familiar detents; any other corner just changes the half-angle.

Questions

What are the miter and bevel for crown molding on a square corner?: For the common 52/38 crown (38° spring angle) cut flat on a compound saw: miter 31.6°, bevel 33.9°. For 45/45 crown: miter 35.3°, bevel 30°. Most compound miter saws have detents at exactly these numbers. Nested upside down against the fence instead, a square corner is a plain 45° miter with no bevel.
How do I find the spring angle of my crown?: Sit a piece in a framing square the way it sits on the wall and ceiling, and measure how far it reaches along each leg: the drop down the wall and the projection across the ceiling. The spring angle is the arctangent of projection ÷ drop. Equal numbers mean 45°; a drop about 1.28 times the projection means 38°.
My corner is not 90°. What changes?: Both angles. Measure the corner with an angle finder, type it in, and the calculator works the compound cut for that corner. A 135° corner on 38° crown is a 14.3° miter and a 17.6° bevel — much gentler than a square corner. Nested, it is a 22.5° miter.
Which edge is the long point?: On an inside corner the bottom edge (the one against the wall) is the long point; on an outside corner the top edge (against the ceiling) is. Cut a test pair from offcuts and hold them in the corner before you cut the real length.

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