Crown Molding Angle Calculator

The two numbers everybody quotes for crown molding — thirty-one point six and thirty-three point nine — are correct for a thirty-eight degree spring angle in a corner of exactly ninety degrees. Drywall corners are almost never exactly ninety degrees, and no two in a room are the same. This calculator takes the spring angle of your moulding and the corner you actually measured, and gives the miter and bevel for that corner. It also gives the setting for cutting the moulding nested against the fence, which needs no bevel at all and is what most finish carpenters do.

Miter angle: 31.6° arctan(sin 38° ÷ tan 45.0°). Set the saw table to this. For cutting the moulding lying flat on the saw — the compound method.
Bevel angle: 33.9° arcsin(cos 38° × cos 45.0°). Set the blade tilt to this. Both settings are needed together — a compound cut is two angles, and either one alone leaves a gap.
A square corner, so the book numbers apply: 31.6° / 33.9° The published figures for 38° spring — 31.6° miter and 33.9° bevel — are calculated for exactly this case and nothing else.
Or skip the compound cut entirely: 45.0° miter, 0° bevel Hold the moulding against the fence at its spring angle — upside down and backwards, ceiling side on the saw table — and a simple miter at half the corner angle produces the same joint with no bevel at all. It is slower to set up, awkward on wide crown, and it is what most finish carpenters actually do, because one setting is harder to get wrong than two.
Inside corner — cope it instead: Miter one, cope the other A mitered inside corner opens as the building moves and as the moulding dries. A coped joint — one piece run into the corner square, the other cut to the profile and fitted over it — closes on itself instead of opening, and tolerates an out-of-square corner without recalculating anything. Miter only the outside corners.
Spring angle: 38° The angle between the back of the moulding and the wall. Most crown is 38/52 or 45/45. Find yours by setting the moulding into a framing square the way it will sit on the wall and reading the angle — do not assume, because the two profiles need visibly different settings.
Material: 5 × 12 ft 60 ft of run at 12 ft per length. Crown wastes more than baseboard because every joint is a compound cut and mistakes cannot be re-cut shorter and used elsewhere as easily. Allow one extra length on any room with more than four corners.
Cut it in the orientation you will fit it: Left and right are not the same A compound cut is handed. The left end of a wall and the right end need mirrored settings, and cutting both the same way produces two pieces that fit the same corner and no piece for the other one. Mark the ceiling edge on every piece before it goes near the saw.

Spring angle is what makes the cut compound

Why crown needs two angles

Baseboard sits flat against the wall, so a corner joint is a single miter at half the corner angle. Crown does not sit flat against anything — it bridges the wall and the ceiling at an angle, the spring angle, and touches each plane along one edge.

Laid flat on a mitre saw table, the moulding is in a different orientation from the one it occupies on the wall. Producing the correct joint from that position requires rotating the table and tilting the blade at the same time: a compound cut.

The two settings come out of the spring angle and the corner angle together. For a thirty-eight degree spring in a square corner they are 31.6 and 33.9 degrees. For forty-five degree spring in the same corner they are 35.3 and 30.0. Those pairs are not interchangeable, and using one profile's numbers on the other leaves a visible gap.

Find the spring angle rather than assuming it. Set the moulding into a framing square the way it will sit on the wall and read where it lands.

The corner is not ninety degrees

Every published crown molding table assumes a right angle, and drywall corners are not right angles. Tape and compound build up in the inside corners, framing moves, and walls are rarely dead straight over their length.

Two or three degrees is normal and it is enough to open a joint. On a painted job that is a caulk line; on stained hardwood it is a visible defect that cannot be fixed after the fact.

Measure each corner with an angle finder and calculate for that corner. Corners in the same room routinely differ by several degrees, so one measurement for the room is not enough.

This is also the strongest argument for coping inside corners rather than mitering them, because a coped joint does not care what the corner angle is.

Nesting, and coping

There is a second way to cut crown that avoids the compound cut entirely. Hold the moulding against the saw fence at its spring angle — upside down and backwards, with the ceiling edge flat on the table — and it is now in the same relative orientation it will occupy on the wall. A simple miter at half the corner angle produces the correct joint, with the blade left square.

It takes a stop or a jig to hold the moulding consistently, and it is awkward on wide crown that will not fit under the blade in that position. In exchange, there is one setting to get right rather than two, and one setting is much harder to get wrong.

Coping is the other traditional answer, and it applies only to inside corners. One piece runs into the corner cut square. The second is mitered to expose its profile, and that profile is then cut away with a coping saw so the piece fits over the face of the first.

A coped joint closes on itself as the building moves, where a mitered inside corner opens. It also absorbs an out-of-square corner without any calculation. Outside corners still have to be mitered, and that is where the numbers above earn their place.

What this is based on

Compound miter geometry — miter = arctan(sin S ÷ tan(C/2)), bevel = arcsin(cos S × cos(C/2))
Standard crown profiles at 38/52 and 45/45 spring angles

Cutting geometry. Saw scales differ in how they label bevel direction, and some saws cannot reach the required bevel in one direction — test every setting on offcuts before cutting finished material.

Frequently asked questions

What are the miter and bevel angles for crown molding?

For a 38 degree spring angle in a square corner, 31.6 degrees miter and 33.9 degrees bevel. For 45 degree spring, 35.3 and 30.0. Those figures assume the corner is exactly 90 degrees, which drywall corners usually are not.

Why do I need both a miter and a bevel?

Because crown does not lie flat against the wall or the ceiling — it bridges both at the spring angle. Cutting it flat on the saw puts it in a different orientation from the one it occupies on the wall, and correcting for that takes a rotation and a tilt together.

What is the spring angle?

The angle between the back of the moulding and the wall when it is in place. Most crown is 38/52 or 45/45. Set the moulding into a framing square the way it will sit and read the angle — the two profiles need visibly different saw settings.

Can I cut crown without a compound angle?

Yes. Held nested against the fence — upside down and backwards, ceiling edge on the table — the moulding is already in its installed orientation, and a simple miter at half the corner angle works with the blade square. It is what most finish carpenters do.

Should inside corners be mitered or coped?

Coped. A mitered inside corner opens as the building moves and as the moulding dries; a coped joint closes on itself and tolerates an out-of-square corner without any recalculation. Outside corners have to be mitered.