How this calculator works
The crown molding goes along the top of every wall, so the feet you need is the distance around the room: twice the length plus twice the width, less any opening. A room has four inside corners, and every bump (a chimney breast or a pillar) adds outside corners. Add an allowance for the angle cuts at the corners and divide by the length of the pieces you buy, rounded up.
Worked example: a room 14 ft long and 12 ft wide has 52 ft of wall. With 10% extra that is 5 pieces of 12 ft (60 ft), with 4 inside corners to cope. With 16 ft pieces you need 4. If 8 ft of the wall is open, it takes 44 ft (5 pieces). Three rooms the same size take 156 ft and 15 pieces, and a large room 20 by 25 ft takes 90 ft and 9 pieces. A chimney breast with two outside corners makes 2 mitered corners.
Crown molding for common rooms (12 ft pieces, 10% extra)
Feet around the room and pieces to buy.
| Room | Feet around | Pieces of 12 ft |
|---|---|---|
| 10 × 10 ft | 40 | 4 |
| 12 × 12 ft | 48 | 5 |
| 12 × 14 ft | 52 | 5 |
| 14 × 16 ft | 60 | 6 |
| 16 × 20 ft | 72 | 7 |
| 20 × 25 ft | 90 | 9 |
Tips before you buy
- Cope the inside corners: a coped joint stays tight when the wood shrinks, and a mitered inside corner opens.
- Cut the molding upside down against the saw fence, in the position it sits on the wall.
- Start with the longest wall that has no door, and work around the room.
- Put the joint of two pieces on a stud, and cut them at 45° so that they overlap.
- Paint or stain before you fix it, and fill the nail holes and the joints at the end.
Tools & materials for this project
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Frequently asked questions
How much crown molding do I need for a room?
The distance around the room plus about 10%: a 14 by 12 ft room has 52 ft of wall and needs 5 pieces of 12 ft.
How do I calculate linear feet of crown molding?
Add the length of every wall that gets molding: twice the length plus twice the width for a rectangular room, which is 52 ft for 14 by 12 ft.
How much extra crown molding should I buy?
About 10% for the corner cuts and mistakes. Buy more if the room has a lot of corners or you are new to cutting it.
Should I cope or miter the corners?
Cope the inside corners (4 in a rectangular room) and miter the outside ones. A coped joint stays tight when the wood moves.
What length of crown molding is best?
Long pieces make fewer joints. 12 ft is common, and 16 ft pieces work for long walls if you can carry them.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.