Crown Molding Calculator
Enter your wall run and your corner angle to get the miter and bevel to set on the saw, plus the linear feet and number of pieces to buy.
How crown molding is cut
Crown molding is not a flat piece of trim, so you do not cut it flat on the saw table. It goes into the saw nested the way it sits on the wall — upside down, with the edge that meets the ceiling flat on the saw table and the edge that meets the wall resting against the fence. Cut it that way and one pair of numbers fits every corner in the room.
Those two numbers are the miter and the bevel. The miter is the angle you swing the saw table to. The bevel is the tilt of the blade. They are not the same number, and that is the part that catches people out: the molding meets the wall at an angle and the corner turns, so the cut has to be tilted and swung at the same time. That is what a compound miter cut means.
For a square 90° corner, the two standard settings are:
- 38° crown — miter 31.6°, bevel 33.9°
- 45° crown — miter 35.3°, bevel 30°
You can also cut crown flat, lying on its back, which uses a different set of numbers and is easier to see what you are doing. It needs a saw with a tall enough fence to stand the molding on edge, and the numbers are not the ones on any chart on this page. Nest the molding instead — it is what the published angles assume.
Spring angle: 38° or 45°
The spring angle is the angle between the back of the molding and the wall when the molding is installed. Almost all crown sold today is one of two profiles:
| Profile size | Usual spring angle |
|---|---|
| 3¼ in | 45° |
| 3⅝ in | 38° |
| 5¼ in | 38° |
| 5½ in and larger | 45° |
Do not take that table as gospel — measure the molding you actually bought. Nest it in the saw the way you intend to cut it and see whether it sits solidly: the edge that meets the ceiling flat on the saw table, the edge that meets the wall against the fence, no rocking. If it rocks, you have the wrong spring angle set. The two figures are 4° apart, and a 4° error on the spring angle opens the joint on every corner in the room, not just one.
Miter and bevel for corner angles other than 90°
Walls are rarely exactly square, and bay windows, angled walls and older houses are nowhere near. Measure the corner with an angle finder and look it up here.
| Corner angle | Miter — 38° crown | Bevel — 38° crown | Miter — 45° crown | Bevel — 45° crown |
|---|---|---|---|---|
| 90° | 31.6° | 33.9° | 35.3° | 30.0° |
| 105° | 38.7° | 28.7° | 42.7° | 25.5° |
| 120° | 46.8° | 23.2° | 50.8° | 20.7° |
| 135° | 56.1° | 17.6° | 59.6° | 15.7° |
| 150° | 66.5° | 11.8° | 69.2° | 10.5° |
Two things to notice in that table. First, the miter and the bevel move in opposite directions: as the corner opens up, the miter gets bigger and the bevel gets smaller. Second, past about 50° of miter you are off the end of the detents on most miter saws. The workaround is to cut the complement from the other side — for a 59.6° miter, set the saw to 30.4° on the other side of zero and flip the workpiece. The cut is identical; you have just moved to the other side of the blade.
Corners, and why the length does not change
A mitered corner consumes no length. You measure each piece to the corner and cut the miter on the end of it, so the material you need is the length along the ceiling, corner to corner. Do not add anything for the corner itself.
Inside and outside corners take the same angles — a 90° inside corner and a 90° outside corner both miter at 31.6° with 38° crown. What changes is the direction: for an outside corner you swing the miter to the opposite side of zero and cut the other end of the stick. It is the same setup made the other way around, and it is the reason a room with outside corners is worth practising on scrap first.
Scarf joints: when a wall is longer than the stick
A 20 ft wall cannot be covered by a 12 ft stick, so the run has to be joined somewhere along its length. That joint is a scarf joint, and doing it well is most of what separates a clean job from a visible one:
- Cut it on an angle, not square. A 45° lap hides the joint inside the profile. A square butt joint shows a straight line across the face of the molding.
- Land it on something solid. A scarf joint must sit over a ceiling joist or a stud, because the two pieces have to be pulled tight to each other. Glue it and nail both sides.
- Put it where nobody looks. Behind a curtain, above a door, on the wall behind the sofa. On a long run you usually get to choose.
This is also the argument for buying longer stock. A 16 ft stick covers more walls without a joint, but long molding is the stock that arrives with a bow in it, and a bowed stick shows a shadow line against the ceiling that no amount of nailing will pull out. Straight 12 ft material beats a bent 16 ft stick every time.
Does the building code cover crown molding?
No. Crown molding is finish carpentry, and the International Residential Code does not regulate it. There is no code figure for the angles on this page — they are geometry, not law, and they come from the profile of the molding, not from a code book.
The only code that touches a ceiling is R305.1, which sets a minimum ceiling height of 7 ft in habitable rooms. Crown molding does not count against that, because it sits at the ceiling line rather than below it.
What actually constrains this work is three things you measure yourself: the corner angle (rarely exactly 90°), the spring angle of the profile you bought (38° or 45°), and the length of the sticks you can handle. All three are worth checking before you cut anything.
Worked example: a 20 × 16 ft room
Take a rectangular room 20 feet by 16 feet, with 38° crown, four inside corners and no outside corners. You are buying 12 ft sticks and allowing 10% waste.
The run along the ceiling is the perimeter: 2 × (20 + 16) = 72 ft. Add 10% waste and you need 79.2 linear ft. In 12 ft sticks that is 6.6 pieces, so you buy 7 pieces, which is 84 linear ft — about 5 ft more than the job needs, and that surplus is what covers a bad cut.
Four inside corners means 8 miter cuts, two at each corner, one on each piece that meets there. The longest wall is 20 ft, so that run needs two pieces with one scarf joint between them.
The saw settings are the ones in the first table: miter 31.6°, bevel 33.9°. Cut a test pair in scrap first — with only 8 cuts to make, a wrong spring angle is the difference between a job that closes up cleanly and one with four open joints you cannot caulk on a stained profile.
Frequently asked questions
What angle do you cut crown molding at?
For a square 90° corner, 38° crown cuts at a miter of 31.6° and a bevel of 33.9°. The same corner in 45° crown cuts at a miter of 35.3° and a bevel of 30°. Both settings assume the molding is nested in the saw at its spring angle — standing upside down with the ceiling edge flat on the saw table and the wall edge against the fence. Cut it flat on its back instead and these numbers do not apply.
How do I know if my crown molding is 38° or 45°?
Set it in the saw the way you intend to cut it and check that it sits solidly — the edge that meets the ceiling flat on the saw table, the edge that meets the wall resting against the fence, no rocking. If it rocks, you have the wrong spring angle. As a starting point, 3⅝ in and 5¼ in profiles are usually 38°, and 3¼ in and most 5½ in and larger profiles are usually 45°, but the profile you actually bought is the only thing that counts. The two settings are 4° apart and the wrong one opens every joint in the room.
Why are the miter and bevel different numbers?
Because the molding is cut at an angle to both the wall and the ceiling at the same time. A flat piece of trim laid against a wall only has to turn in one plane, so its miter alone does the work. Crown leans back at its spring angle, and the corner turns in the horizontal plane, so the cut has to be tilted and swung at once — a compound miter. That is why a miter saw doing crown work uses both scales together, and why the two numbers never match.
Can I cut crown molding flat instead of nested?
You can, and some people find it easier to see the cut. Lying the molding on its back on the saw table uses a completely different set of angles — the numbers in the charts here do not apply. It also needs a saw with enough capacity to stand the molding on edge without the blade fouling the fence, which rules out most small saws on 5¼ in and larger profiles. Nesting is what the published angles assume, and it is the method to use if you want to work from a chart.
How much crown molding do I need for a 12 × 12 room?
The run is the perimeter, 4 × 12 = 48 ft. Add 10% waste for 52.8 linear ft. In 12 ft sticks that is 4.4 pieces, so you buy 5 sticks, or 60 linear ft. You would make 8 miter cuts at the four corners. If the room has outside corners, a bay window or walls that are not square, go to 15% waste instead — the extra cuts are where material gets eaten.
How much waste should I allow for crown molding?
10% for a plain square room with four corners and no joins. 15% where there are outside corners, bay windows, angled walls or a lot of scarf joints. Go higher again if the molding has a deep profile that is hard to line up, or if you are staining rather than painting — you cannot hide a bad joint with caulk and paint. Waste on crown is not really waste; it is the cost of the test cuts that tell you the spring angle was right.
Do inside and outside corners use the same angles?
Yes. A 90° inside corner and a 90° outside corner both cut at a miter of 31.6° and a bevel of 33.9° in 38° crown. What changes is which side of the blade the cut is on: for an outside corner you swing the miter to the other side of zero and cut the opposite end of the stick. Same numbers, same setup, mirrored.
How do I join crown molding on a wall that is too long for one stick?
Cut a scarf joint on a 45° angle rather than square, so the joint sits inside the profile instead of showing as a straight line across the face. Land it over a ceiling joist or a stud so both pieces can be pulled tight, glue it, and nail both sides. Then place it where it will not be looked at — behind a curtain or above a doorway. If you would rather not make the joint at all, buy longer stock, but check the sticks for bow before you pay for them.