Baseboard Trim Calculator
| Room | Doors | Net run | Sticks (10 ft) | Buy |
|---|---|---|---|---|
| Bedroom 12 x 12 | 1 | 45 ft | 5 | 50 ft |
| Living room 15 x 20 | 3 | 61 ft | 7 | 67 ft |
| Great room 20 x 24 | 4 | 76 ft | 9 | 84 ft |
| Office 11 x 13 | 2 | 42 ft | 5 | 46 ft |
Baseboard is linear-foot math with two deductions and one allowance. The raw run is the room perimeter - twice the length plus twice the width - then every doorway takes its width out of the run (about 3 feet each), and casing covers the jamb so no baseboard goes there. What is left is the net run; add 10 percent for the cuts, because every corner is a 45-degree miter (or a coped joint on inside corners, the pro move that survives wall movement better than any miter).
Stock length decides the piece count, and short stock is false economy. Trim comes in 8, 10, 12 and 16-foot sticks; a 10-footer spans most wall runs in one piece, and every splice you avoid is a joint that never telegraphs through paint a year later. Buy the longest stock your vehicle carries: the price per foot barely moves, and a 15-by-20 room in 8-foot stock means nine pieces and four extra splices against seven pieces in 10-foot.
How to use
- Measure the room perimeter - twice length plus twice width - and count the doorways.
- Subtract about 3 feet per door for the cased opening; the calculator handles it.
- Order pieces at 10-foot stock with a 10 percent cut allowance; cope inside corners, miter the outside.
Frequently asked questions
How do I calculate how much baseboard I need?
Perimeter minus doors: a 15-by-20 room is 70 linear feet around, minus about 9 feet for three doors, so 61 net feet. Add the 10 percent cut allowance and order about 67 feet - seven 10-foot sticks. The perimeter is just 2 × (length + width); the deductions are what people forget.
How much baseboard do I deduct for a door?
About 3 feet - the standard 36-inch cased opening plus a bit of casing on each jamb. Count every doorway in the run including closet openings, and skip nothing else: baseboard runs through behind radiators and built-ins gets trimmed on site, not in the order.
Should inside corners be coped or mitered?
Coped - the pro answer. Inside walls are never truly 90 degrees, so a mitered inside corner opens a gap that paint cannot hide; a cope cuts one board to the profile of the other and stays tight as the house moves. Outside corners are mitered 45-plus-45 because nothing moves against them. Cope the inside corners and your joints outlast the paint cycle.
What height baseboard should I use?
Ceiling height sets it: 8-foot ceilings carry 3.25 to 4.5-inch baseboard, 9-foot and up takes 5 to 7 inches or a two-piece build-up. Proportion is the rule - taller rooms swallow short base, and skinny 2.25-inch trim under a 9-foot ceiling reads as an afterthought. Door casings usually run a quarter to half inch thicker than the base so the profiles read as a family.
How much extra trim should I buy?
10 percent covers the miter and cope cuts plus one misfire per room. Trim is sold by the stick, not partly, so the piece count rounds up anyway - a 61-foot net run at 10-foot stock is 6.7 sticks, which rounds to 7, and the 10 percent is already satisfied. Keep one offcut; patched nail holes touch up better than a mismatched replacement.
Can I install baseboard over carpet?
No - trim goes down on the subfloor before carpet, held up about 3/8 of an inch so the carpet tucks under it. Installing over carpet leaves a shadow gap when the carpet is replaced later. For hardwood, leave the same reveal gap so the floor can move; the baseboard shoe or quarter-round hides it either way.