How trim is measured
Baseboard runs around the edge of the room, so you start with the perimeter: two times the length plus two times the width. Door openings don't get baseboard, so their widths come out. A waste allowance covers the mitered and coped corners.
The same math works for quarter round and shoe molding. For crown molding, set doors to zero, since crown runs straight across above the door.
Worked example: a 14 × 12 room with one door
- Perimeter: 14 + 12 + 14 + 12 = 52 ft
- Minus a 3 ft door: 49 ft
- Add 10%: about 54 linear ft
- In 16 ft pieces: 4 pieces
Buy long pieces
Every joint along a wall is a spot that can open up as the house moves through the seasons. The cleanest trim jobs use one piece per wall wherever possible. If your longest wall is 14 feet, 16-foot pieces let you run it in one go, and the offcuts often cover short walls and closet returns.
The piece count here is based on total footage. If you want no joints at all, list each wall and make sure you have a piece at least that long for it.
A few finishing tips
- Cope inside corners instead of mitering them. A coped joint stays tight when the walls aren't quite square.
- Miter outside corners and glue them as well as nailing.
- Prime and paint trim before you put it up. Afterward you only need to touch up the nail holes.
Putting in new flooring at the same time? Get your box count from the flooring calculator.
Frequently asked questions
How do I calculate linear feet of baseboard?
Add up the lengths of all the walls, then subtract the width of each doorway. For a 12 by 12 room with one 3-foot door, that's 48 minus 3, or 45 linear feet.
How much extra baseboard should I buy?
About 10 percent for a simple room and 15 percent for rooms with many corners, angled walls or columns.
What length of baseboard should I buy?
Buy pieces long enough to cover your longest wall in one run if you can. Sixteen-foot lengths are common for that reason, but make sure you can get them into the house.
Can I use this calculator for crown molding?
Yes. Set door openings to zero, because crown runs over doors. Add a little more waste if you're new to cutting crown, since the compound angles take practice.
Results are estimates for planning. Product coverage, site conditions and installation methods vary, so check manufacturer guidance before you buy.