Crown molding runs around the top of every wall, including across doorways, so it is measured from the full perimeter of the room. Enter the room size; the calculator adds extra for the miter and coped joints and gives the number of pieces.
How to use the calculator
- Measure the length and width of the room along the walls.
- Enter the number of doorways and their width; trim does not run across an opening.
- Choose the waste allowance and the length of the pieces sold at your store.
Formula
Wall length = 2 × (length + width) − doorways × doorway width Linear feet to buy = wall length × (1 + waste %) Pieces = linear feet ÷ piece length, rounded up
Worked example: a 14 × 12 ft room
- Perimeter: 2 × (14 + 12) = 52 ft (doorways are not deducted; crown runs above them).
- Add 15% waste: 59.8 ft.
- In 8 ft pieces: 8 pieces, or 5 pieces of 12 ft.
Why crown needs more waste than baseboard
Crown is cut at a compound angle and is easy to get wrong, especially on the first corners. Using 15% instead of 10% leaves room for test cuts. Buy long pieces where you can; a splice in the middle of a wall is harder to hide on crown than on baseboard.
Questions
Do I subtract doorways for crown molding?
No. Leave the doorways at 0, because crown runs along the ceiling above them.
How much crown for a 12 × 12 room?
48 ft of wall plus 15% is 55.2 ft, or 7 pieces of 8 ft.
What about vaulted ceilings?
Measure each wall along the line where the crown will sit and enter the total as the length with a width of 0.
Sources
- NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, National Institute of Standards and Technology.
Used for: Exact foot and inch definitions.