Crown Molding Calculator — Lengths, Miter and Bevel
Crown is measured like baseboard and cut like nothing else. This gives you the lengths to buy and the exact miter and bevel settings for cutting it flat on the saw — the two numbers that decide whether the corners close.
Take this list to the store
We'll email the quantities above, what you typed in, and a link that reopens this calculator already filled in — so you can adjust it on your phone in the aisle.
How to work it out
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Measure the ceiling, not the floor
Crown follows the line where the wall meets the ceiling, so measure up there. In most rooms it is the same as the floor perimeter, but not always — a bulkhead, a soffit over the cabinets or a dropped section changes the path the molding takes.
Unlike baseboard, you do not deduct doorways. Crown runs straight over the top of them.
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Enter each rectangle separately
An L-shaped room is two rectangles. Add a section for each and the calculator totals the perimeter correctly — including the two extra corners the L creates, which is exactly where crown orders come up short.
Count your corners while you are at it. You will need to know how many are inside and how many are outside before you start cutting.
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Find the spring angle before you buy anything
Stand a short cut-off on a flat table with its back edges touching the table and a square. The angle between the back of the molding and the vertical face is the spring angle. Most US crown is 38 degrees; the other common one is 45.
Get this wrong and every cut is wrong. It is the single most important number in the whole job, and it is printed on almost no packaging.
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Cut it flat and set both angles
You can cut crown standing up against the saw fence, held at its spring angle — the traditional method, and it only works if your saw is tall enough. Cutting it flat on the table is easier and more repeatable, but it needs a compound cut: a miter and a bevel together.
The two numbers above are those settings. For standard 38 degree crown in a square corner they are 31.6 and 33.9 — set them once and every corner in the room is the same cut, mirrored.
Miter and bevel settings for cutting crown flat
Set the miter and the bevel to these figures. The same pair works for inside and outside corners — you change which side of the line you cut, not the angles.
| Spring angle | Corner 90° (square) | Corner 135° (obtuse) | Corner 45° (acute) |
|---|---|---|---|
| 38° / 52° | 31.6° miter, 33.9° bevel | 56.1° miter, 17.6° bevel | 14.3° miter, 46.7° bevel |
| 45° / 45° | 35.3° miter, 30.0° bevel | 59.6° miter, 15.7° bevel | 16.3° miter, 40.8° bevel |
| 52° / 38° | 38.2° miter, 25.8° bevel | 62.3° miter, 13.6° bevel | 18.1° miter, 34.7° bevel |
Cut a test pair in scrap before you touch the real molding — every saw reads slightly differently. Note that very obtuse corners need miter settings beyond 50°, which is past the range of many saws; those corners have to be cut standing up against the fence instead.
Crown molding by room size
Perimeter and lengths to buy, with a 15% allowance.
| Room | Perimeter | Order | 8 ft lengths | 12 ft lengths |
|---|---|---|---|---|
| 10 × 10 ft | 40 ft | 46 ft | 6 | 4 |
| 12 × 12 ft | 48 ft | 56 ft | 7 | 5 |
| 12 × 14 ft | 52 ft | 60 ft | 8 | 5 |
| 14 × 16 ft | 60 ft | 69 ft | 9 | 6 |
| 16 × 20 ft | 72 ft | 83 ft | 11 | 7 |
| 20 × 24 ft | 88 ft | 102 ft | 13 | 9 |
Buying longer stock almost always means fewer pieces and fewer joints in the middle of a wall.
How much crown molding for a 12x14 room?
The perimeter is 2 × (12 + 14) = 52 linear feet. Crown runs over doorways so nothing gets deducted. With a 15% allowance that is 60 feet to buy, which is five 12 ft lengths or eight 8 ft lengths.
Five twelve-foot pieces is the better order. The room has two 14 ft walls, and a 12 ft length will not run one of them in a single piece — but with five pieces you can put the scarf joint on a wall that is less visible from the door, rather than being forced into four joints.
Spring angle: the number that decides everything
Crown molding sits at an angle, bridging the wall and the ceiling. The spring angle is how far it leans — measured between the back of the molding and the wall. Standard American crown is 38 degrees to the wall and 52 to the ceiling, usually written 38/52. The other common one is 45/45, which sits symmetrically.
To find yours, take a short cut-off and stand it on a flat table the way it will sit on the wall, with both back edges touching. Put a square against it. The angle between the molding's back and the vertical leg of the square is the spring angle.
This matters because every compound cut depends on it. A 38 degree crown cut with 45 degree settings will leave a gap you cannot caulk away. If the molding came without documentation, measure it — do not guess.
Where the miter and bevel numbers come from
When crown is cut flat on the saw table, the blade has to slice through a piece that will later be tilted. That takes two movements at once: the saw head swings sideways (the miter) and tilts over (the bevel).
The two settings come from the spring angle S and the corner angle C:
- Miter = arctan( sin S × tan(C ÷ 2) )
- Bevel = arcsin( cos S × cos(C ÷ 2) )
For 38 degree crown in a square corner that gives 31.62 and 33.86 — the familiar 31.6 and 33.9 printed on the detents of most miter saws. The calculator runs the same arithmetic for whatever corner you actually measured, which is the useful part: real rooms are rarely 90 degrees.
Measure your corners before you trust 90
Almost no room is square. Drywall builds up in the corners, houses settle, and a corner that measures 92 degrees is completely ordinary. Cut both pieces at the 90 degree setting and you get a gap at the top of the joint that opens as the caulk shrinks.
An angle finder or a digital protractor costs very little and takes the guesswork out. Measure each corner, enter it, and cut that corner to its own numbers. If you have a room where every corner differs, label your pieces as you cut — it is the only way to keep track.
A shortcut worth knowing: if a corner is out by a degree or two and you are painting the crown, cutting both halves at half the measured angle and easing the joint with a block plane will close it. If the crown is stained, you need the real numbers.
Coping instead of mitering inside corners
Professional trim carpenters usually do not miter inside corners at all. They cut the first piece square into the corner, then cope the second — cutting along the profile with a coping saw so it nests over the face of the first.
The reason is movement. A mitered inside corner opens up as the house dries out and the wood shrinks, and the gap appears right at eye level. A coped joint closes onto itself and hides seasonal movement almost completely.
Coping takes practice and does not change the quantities at all, so the material list above holds either way. Outside corners still get mitered — there is no coping an outside corner.
Buy long, and buy a spare
The most useful thing you can do for a crown job is order stock long enough to run each wall in one piece. Every joint in the middle of a wall is a scarf cut that has to be glued, nailed into a stud and sanded, and it will always be slightly visible in raking light.
Add one full length beyond what the calculator says. Crown is long, thin and easy to damage, the profile you chose may be discontinued next month, and the first corner you cut is almost never the one you keep. A spare length costs a fraction of a second delivery run.
Check the profile matches across boxes before you leave the store. Crown from different production runs can differ enough in profile depth to show at a joint.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
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perimeter = 2 × (length + width), summed over every sectionL-shaped rooms total correctly, including the extra corners. -
× (1 + waste ÷ 100)15% standard — crown cut-offs are rarely long enough to reuse. -
lengths = order ÷ stock length, rounded upYou buy whole pieces, not linear feet. -
miter = arctan( sin S × tan(C ÷ 2) )S is the spring angle, C the corner. For 38° crown in a square corner: 31.6°. -
bevel = arcsin( cos S × cos(C ÷ 2) )The saw tilt that goes with that miter. For 38° crown in a square corner: 33.9°. -
nails ≈ order ÷ 1.33A finish nail roughly every 16 inches into the framing.
Common questions
What are the miter and bevel angles for crown molding?
For standard 38 degree crown in a square corner, cut flat on the saw: miter 31.6°, bevel 33.9°. For 45 degree crown it is 35.3° and 30.0°. Change the corner angle and both numbers change — that is what the calculator above is for.
How do I find the spring angle of my crown?
Stand a short cut-off on a flat table the way it will sit on the wall, with both back edges touching the table and a square. The angle between the back of the molding and the vertical face of the square is the spring angle. Most US crown is 38 degrees.
Do I deduct doorways from crown molding?
No. Crown runs along the ceiling, straight over the top of every door and window. That is the main difference from baseboard, where you do deduct openings.
Should I cut crown flat or standing up?
Flat is easier to hold and repeat, but needs a compound cut — both a miter and a bevel. Standing it against the fence at its spring angle uses a single miter setting, which is simpler arithmetic but needs a tall enough saw and a steady hand. Most people find flat more accurate once the settings are dialled in.
How much waste should I allow for crown molding?
Fifteen per cent for a normal room. Crown cut-offs are almost never reusable because each end already carries a compound angle, so the leftovers pile up faster than with baseboard. Go to 20% for a room with many corners or a molding with a directional pattern.
Why won't my corners close?
Usually one of three things: the corner is not actually 90 degrees, the spring angle you used is wrong, or the molding was not held tight against both fences when you cut it. Measure the corner with an angle finder and check the spring angle on an cut-off before blaming the saw.
Can I install crown molding on a ceiling that isn't level?
Yes, and most ceilings are not. Crown follows the ceiling rather than a level line, so small waves disappear. Bigger dips get closed by pushing the molding up tight and caulking the top edge — which is why crown is usually painted, and why it hides ceiling problems far better than it hides its own bad joints.
What size crown molding should I use?
Roughly, a rule of thumb ties it to ceiling height: around 3 to 4 inches for 8 ft ceilings, 5 to 7 inches for 9 to 10 ft, and larger built-up profiles above that. It is a proportion judgment rather than a rule — hold a sample up in the actual room before committing.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- Standard compound miter geometry — the arctan and arcsin relations for spring and corner angle
- Miter saw manufacturer crown detent settings — the 31.6° / 33.9° pairing used as a cross-check
- Wood Molding and Millwork Producers Association profiles — standard 38/52 and 45/45 spring angles
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 12, 2026.