Baseboard Length Calculator
Baseboard, the trim that runs along the bottom of your walls, is sold by the linear foot, so the only thing you really need to know is how many feet of wall it has to cover. This calculator works that out. Enter the room length and width and the total width of your door openings, and the tool adds twice the length and twice the width to find the room perimeter, then subtracts the door openings (which get no baseboard) to give the net linear feet of trim you need. The perimeter is the distance all the way around the floor, and doorways break that run, so subtracting their combined width gives the true length of baseboard required. Windows normally sit above the baseboard and are not subtracted. Every input is editable, so you can model a different room, more doorways, or an open plan. The result is the net length; for a real order, add a small waste allowance of 5 to 10 percent for miter cuts and the odd miscut, then round up to whole boards. Every figure is computed deterministically from the formula shown below, with a worked example that reconciles exactly to the calculator's defaults so you can follow each step before you buy.
Baseboard length is the room perimeter minus the door openings: 2 x (length + width) - door openings. A 12 x 14 room has a 52 ft perimeter, and after subtracting 3 ft of doorways you need 49.00 linear feet of baseboard.
Baseboard length formula
Perimeter = 2 x ( length + width )
Baseboard length = perimeter - door openings
length, width = room dimensions in feet
door openings = combined width of all doorways in feet
Add twice the length and twice the width for the perimeter, then subtract the total doorway width. The result is the net linear feet of baseboard. Add waste before buying.
Worked example
Suppose a room is 12 by 14 feet with a single 3-foot doorway.
- Perimeter = 2 x (12 + 14) = 2 x 26 = 52 ft
- Door openings = 3 ft
- Baseboard length = 52 - 3 = 49.00 ft
You need 49.00 linear feet of baseboard (before a waste allowance). These are the calculator's default inputs, so the result above matches the widget exactly.
Baseboard length by room size
Net length for a single 3-foot doorway at a few room sizes.
| Room (ft) | Perimeter | Baseboard length |
|---|---|---|
| 10 x 10 | 40 ft | 37.00 ft |
| 12 x 14 | 52 ft | 49.00 ft |
| 14 x 16 | 60 ft | 57.00 ft |
| 16 x 20 | 72 ft | 69.00 ft |
Add 5 to 10% for miter cuts and waste, then round up to whole boards.
Baseboard length calculator: frequently asked questions
How do I work out how much baseboard I need?
Find the room perimeter by adding twice the length and twice the width, then subtract the total width of door openings, which do not get baseboard. Baseboard length = perimeter minus door openings. The result is the linear feet of trim to buy. Add a small allowance for miter cuts and waste, and round up to whole boards.
Do I subtract doorways?
Yes. Baseboard runs along the base of walls but stops at door openings, so the width of each doorway is not covered. Add up the widths of all door openings and subtract that total from the room perimeter. Windows usually sit above the baseboard, so they are not subtracted unless a feature runs to the floor.
Should I add extra for waste?
Yes. Miter cuts at corners, the occasional miscut and matching profiles between boards all consume a little extra length. Adding 5 to 10 percent to the calculated length, then rounding up to whole boards, is a sensible margin. The base calculation here gives the net length; add your own waste allowance before buying.
What is a linear foot?
A linear foot is simply one foot of length, measured in a straight line, regardless of width or thickness. Baseboard and other trim are sold by the linear foot or in fixed board lengths, so the total length you need is expressed in linear feet. It is a measure of length only, not area.
How do I handle an irregular room?
For an L-shaped or irregular room, the perimeter is the sum of all wall lengths around the floor, not just twice the length plus twice the width. Measure each wall and add them up, then subtract the door openings. Enter dimensions that reproduce the true perimeter, or total the wall lengths separately and subtract doors.
Official sources
- Length and perimeter measurement reference: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.