How this calculator works
Baseboard runs along every wall except across doorways, so the length is the room perimeter minus the width of each doorway. Crown molding runs the full perimeter. We add a waste allowance for mitre cuts and mistakes, and divide by the board length.
Worked example: a 12 × 14 ft room has a 52 ft perimeter. With two 3 ft doorways, that is 46 ft of baseboard, or 50.6 ft with 10% waste, which is 7 boards of 8 ft. Crown molding for the full perimeter is 57.2 ft with waste, which is 8 boards.
Tips before you buy
- Cope the inside corners (shape one board to fit over the other) rather than mitring them. They stay tight when the wood shrinks.
- Nail into the studs, not just the drywall, and caulk the top edge and fill the nail holes before painting.
- Let the trim acclimate in the room for a day or two before you cut it.
- Start with the longest, straightest wall and work around the room so that short pieces end up in less visible places.
Tools & materials for this project
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Frequently asked questions
How do I calculate baseboard for a room?
Add up the length of all the walls and subtract the doorways. For a rectangle that is 2 × (length + width) minus the width of each door opening. Add 10% for waste.
How much extra baseboard should I buy?
10% is standard, to cover mitre cuts and mistakes. For rooms with a lot of corners or when matching a pattern, 15% is safer.
How many pieces of baseboard do I need for a 12x12 room?
A 12 × 12 ft room has a 48 ft perimeter. With two 3 ft doorways that is 42 ft, or 46 ft with waste, so 6 boards of 8 ft.
Related calculators & guides
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.