Crown Molding Calculator — How Much Trim Do I Need?
Enter your room length, width and corner counts to get crown molding linear feet, boards and coping notes. No sign-up, no data stored.
Crown molding plan
How crown molding is estimated
- Perimeter = 2 × (length + width). A 12×14 room = 52 ft.
- Waste = +10% for miters, copes and miscuts — more for stained wood (can't patch), less for painted.
- Boards = perimeter ÷ board length, rounded up per wall run, then summed.
- Corners: inside corners get coped (square piece + back-cut profile); outside corners get 45° miters.
Crown is installed upside-down and backwards on the saw — cut with the top of the molding against the fence, or use a crown jig. Measure each wall separately rather than trusting the room's nominal dimensions; walls are rarely square.
Room size → crown length reference
Perimeter and 10%-waste purchase for common rooms.
| Room | Perimeter | Buy (10% waste) | 12-ft boards |
|---|---|---|---|
| 10×10 | 40 ft | 44 ft | 4 |
| 10×12 | 44 ft | 48 ft | 4 |
| 12×12 | 48 ft | 53 ft | 5 |
| 12×14 | 52 ft | 57 ft | 5 |
| 14×18 | 64 ft | 70 ft | 6 |
Last updated: October 2026 · Estimates assume rectangular rooms at the ceiling line. Add every wall notch, bay window and built-in to the perimeter — they each eat molding.
Crown molding FAQ
Yes, with a miter saw and a coping saw — but the coping cut is the skill. Practice on scrap until the profile matches, then work corner to corner with the longest pieces first.
Most stock crown is 38/52; some profiles are 45/45. Measure the angle between the back of the molding and the wall — or set your saw to 38/52 and test-fit a corner.
Both: a bead of adhesive on the wall, then 1-1/4-in finish nails through the top and bottom of the molding. Nail into studs where you can; adhesive carries the rest.
Coped joints shouldn't gap — if one does, it's usually a coping cut that's too square. Re-cut the back at a steeper angle (about 45°) so only the front edge of the profile touches.
Use 3-1/2- to 4-in crown on 9-ft ceilings and 5-1/2-in on 10-ft+ — bigger rooms want proportionally bolder trim. A 2-1/2-in crown on a tall ceiling reads as baseboard.
Related calculators & guides
How Much Crown Molding Do I Need?
Perimeter math, coping vs miter, and spring angles for clean corners.
Read the guide →