📏 Trim & Molding Calculator
Enter the room dimensions and door count, and get the baseboard and crown molding lengths (with waste) plus how many stock pieces to buy.
Baseboard length (+waste)
45.5 ft
4 × 12 ft pieces
Crown / ceiling trim (+waste)
48.4 ft
5 pieces · full perimeter
Room perimeter
44 ft
Baseboard = perimeter − door openings; crown/picture rail uses the full perimeter (it runs over doors). Add 10% for mitre cuts and mistakes, and round up to whole sticks. 🔒 In your browser.
How the trim & molding calculator works
Trim runs around the room perimeter, which is 2 × (length + width). Baseboard stops at each door opening, so the tool subtracts the total door width; crown molding and picture rail run continuously above the doors, so they use the full perimeter. It then adds your waste percentage for mitre cuts and mistakes and divides by your stock length, rounding up to whole pieces.
Add about 10% waste for a simple room and more where there are many corners, since each inside and outside mitre wastes a little material. Buy from the same batch and profile, and remember that long walls may need a scarf joint between two pieces. This estimates length only, not the exact cut list.
Frequently asked questions
How much baseboard do I need?
Measure the room perimeter (2 × (length + width)), subtract the width of each door opening, and add about 10% for waste. For a 12 × 10 ft room with one 32-inch door that’s roughly (44 − 2.67) × 1.10 ≈ 45.5 ft.
Does crown molding subtract doors?
No — crown molding, picture rail and cove run continuously around the top of the room, over the doors, so they use the full perimeter. Only baseboard and chair rail stop at door openings.
How much extra trim should I buy?
About 10% for a straightforward room, more (up to 15%) where there are lots of corners, a complex profile or long walls needing joints. Mitre cuts at every corner waste a little material each time.
How do I work out how many pieces to buy?
Divide the total length needed (including waste) by the length of one stock piece and round up. For 45 ft of trim in 12 ft lengths that’s 45 ÷ 12 = 3.75, so buy 4 pieces.
What is a scarf joint?
An angled joint used to join two pieces of trim end-to-end on a wall longer than a single stock length. Cut both ends at 45° so they overlap; it hides the seam better than a straight butt joint.