Crown Molding Calculator
Calculate how many linear feet of crown molding a room needs and how many 8, 12 or 16 ft pieces to buy, with inside and outside corner counts, finish nails and cost.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Crown molding needed
- 52 ft
- 52 ft room perimeter plus 0 ft of extra runs. 57.2 ft with 10% waste.
- Pieces to buy
- 4 pieces of 16 ft
- 64 ft purchased. Longer pieces mean fewer scarf joints on a wall
- Corner cuts
- 4 corners
- 4 inside corners to cope, 0 outside corners to miter
- Finish nails
- 78 nails
- Two 2 to 2.5 in (5 to 6 cm) 15 or 16 gauge nails every 16 in, one into the wall and one into the ceiling framing
Crown Molding formula
Linear feet = 2 x (Room length + Room width) + extra runs
Order length = Linear feet x (1 + waste %)
Pieces = Order length / piece length, rounded up
Nails = Linear feet x 12 / 16 x 2Worked example
A 16 x 20 ft living room with a 5 ft soffit run, six inside corners and two outside corners, using 12 ft pieces with 15% waste: perimeter = 2 x (16 + 20) = 72 ft, plus 5 ft = 77 ft. With waste: 77 x 1.15 = 88.55 ft. 88.55 / 12 = 7.4, so buy 8 pieces of 12 ft, which is 96 ft of molding.
Nails: 77 x 12 / 16 = 57.75, rounded up to 58 nailing points, times 2 = 116 finish nails. At $3.50 per foot the 96 ft purchased costs $336.
Quick reference
| Room | Perimeter | With 10% waste | 16 ft pieces | 8 ft pieces |
|---|---|---|---|---|
| 10 x 10 ft | 40 ft | 44 ft | 3 | 6 |
| 10 x 12 ft | 44 ft | 48.4 ft | 4 | 7 |
| 12 x 12 ft | 48 ft | 52.8 ft | 4 | 7 |
| 12 x 14 ft | 52 ft | 57.2 ft | 4 | 8 |
| 14 x 16 ft | 60 ft | 66 ft | 5 | 9 |
| 16 x 20 ft | 72 ft | 79.2 ft | 5 | 10 |
| 20 x 20 ft | 80 ft | 88 ft | 6 | 11 |
Coping vs mitering corners
Outside corners are mitered: both pieces are cut at 45 degrees (or half of whatever the true angle is) and meet point to point. Inside corners are usually coped instead. The first piece runs square into the corner; the second is cut at 45 degrees, then the profile is traced with a coping saw along the miter line and back-cut so only a thin edge touches the first piece. A coped joint hides a corner that is out of square and stays closed as the wood moves through the seasons, where a mitered inside corner opens up.
Plan the order so you cope toward the door: start with the wall opposite the entry, cut square on both ends, then work around the room so each new piece is coped on one end and square or mitered on the other. Buy pieces long enough to span each wall; where a splice is unavoidable, cut a 45 degree scarf joint over a stud and glue it.
Spring angle and saw settings
Crown does not sit flat on the wall; it leans out at its spring angle, either 38 degrees (sometimes labeled 38/52) or 45 degrees (45/45). Check yours with a square before cutting, because the compound miter settings depend on it. The simplest method is to cut the molding nested, upside down against the saw fence at the same angle it sits on the wall, and use a plain 45 degree miter. Cutting flat on the saw table needs a compound setting: 31.6 degrees miter and 33.9 degrees bevel for 38 degree crown, or 35.3 and 30 for 45 degree crown.
Nail into the wall studs and the ceiling joists, or, where the joists run parallel to the wall, into a beveled backer strip screwed to the top plate. Two nails every 16 in is the normal pattern. Fill nail holes, caulk the top and bottom edges, and prime before painting; MDF crown should be primed on the cut ends as well so they do not swell.
Key facts
- Crown molding is sold in 8, 12 and 16 ft lengths; a 16 ft piece spans most walls without a scarf joint.
- Most crown has a 38 or 45 degree spring angle, the angle the molding leans off the wall, and the two need different saw settings.
- For 38 degree crown cut flat on the saw, a square inside corner takes a 31.6 degree miter and a 33.9 degree bevel; 45 degree crown takes 35.3 and 30.
- A 3-5/8 in crown suits an 8 ft ceiling; 4-1/2 to 5-1/4 in looks right at 9 to 10 ft.
- Inside corners are usually coped rather than mitered because a coped joint stays tight when the wood shrinks or the corner is not 90 degrees.
Frequently asked questions
How many feet of crown molding do I need for a 12 x 14 room?
The perimeter is 2 x (12 + 14) = 52 ft. Add 10% for waste and you need 57.2 ft, which is 4 pieces of 16 ft or 8 pieces of 8 ft.
Should I cope or miter crown molding?
Miter outside corners and cope inside corners. Coping takes longer to learn but stays tight when the room is out of square and when the wood shrinks in winter, which a mitered inside corner does not.
What size crown molding should I use?
About 3-5/8 in for a standard 8 ft ceiling, 4-1/2 to 5-1/4 in for 9 to 10 ft ceilings, and larger built-up profiles above that. Very tall crown on a low ceiling makes a room feel shorter.
What angle do I cut crown molding at?
Nested upside down in the saw, a square corner is a plain 45 degree miter. Cut flat, 38 degree spring crown needs a 31.6 degree miter with a 33.9 degree bevel, and 45 degree crown needs 35.3 and 30.
Sources and references
Next steps for this project
The usual order for a paint & walls project. See all paint & walls calculators.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.