Crown Molding Calculator
Calculate how much crown molding you need for a room.
Enter the room perimeter and number of corners to plan your purchase.
Crown molding is a decorative trim installed at the junction where walls meet the ceiling. Calculating materials correctly requires measuring the room perimeter accurately, choosing the right board lengths to minimize waste, and accounting for the angled cuts at every corner.
Core formula:
Total Linear Footage = Perimeter of Room (where molding is installed)
Boards Needed = CEILING(Total Length / Board Length) (always round up)
Material with Waste = Total Length × (1 + Waste Factor)
Measuring the room perimeter:
- Measure each wall where molding will be installed, including walls with doorways
- Subtract the width of each doorway opening from the wall where it falls
- Add all adjusted wall lengths together
Standard molding board lengths:
| Market | Common Lengths |
|---|---|
| US (Imperial) | 8 ft, 12 ft, 16 ft |
| Canada / Metric | 2.4 m, 3.0 m, 3.6 m, 4.8 m |
Longer boards are almost always better — they span corners and feature walls without a seam, and are usually priced proportionally (buying one 16 ft board is equivalent to two 8 ft boards in price).
Waste factor recommendations:
| Room Complexity | Waste Factor |
|---|---|
| Simple rectangular room | 5–8% |
| L-shaped or offset room | 10–12% |
| Many corners, bay windows | 12–18% |
| First-time installer | Add extra 10% |
Why corners waste material: Crown molding must be cut at angles at every corner. An inside corner cut (where two walls meet at 90°) wastes approximately 4–8 inches per piece. An outside corner (convex projection) wastes even more because both pieces are mitered. A room with 8 corners will have 8 pairs of angled cuts — each pair wasting 6–12 inches of material.
Crown molding spring angle: Crown molding sits at an angle between the wall and ceiling — typically 38/52° or 45/45° (these refer to the angle of the molding against the wall/ceiling). This spring angle determines the correct miter and bevel settings on your miter saw. For 38/52° molding, inside corners use: miter 31.6°, bevel 33.9° (each piece).
Cost reference (2025):
| Material | Cost per Linear Foot |
|---|---|
| Polystyrene foam | $0.50–$1.50 |
| MDF (painted) | $1.00–$3.00 |
| Finger-jointed pine | $1.50–$3.50 |
| Solid poplar | $2.50–$5.00 |
| Solid oak or cherry | $4.00–$10.00+ |
Worked example: Rectangular room: 14 × 18 ft (56 ft perimeter), one doorway 32 inches wide. Adjusted perimeter = 56 − (32/12) = 56 − 2.67 = 53.3 linear feet With 10% waste: 53.3 × 1.10 = 58.6 linear feet needed Using 12 ft boards: ⌈58.6 / 12⌉ = 5 boards (60 ft — 1.4 ft remaining for corner fixes)