Baseboard goes along the base of a wall, so the number you need is a length. It is not the room’s floor area, and the two are easy to mix up because both come from the same two measurements.
Perimeter of a rectangular room = 2 × (length + width)
Net run = perimeter − widths of openings the trim stops at
Several rooms: add their runs
Square feet versus linear feet
A 14 × 12 ft room has a floor of 14 × 12 = 168 sq ft, but its walls run 52 ft. Flooring is bought by the first number and baseboard by the second. The floor area does not tell you how much trim a room takes.
Doorways and openings
Baseboard stops at a doorway, so the width of each opening it does not cross comes off the perimeter. With 6 ft of doorways the run of that room is 46 ft. Crown and other trim that runs the full perimeter does not stop at doors, so the planner’s crown mode leaves openings alone. Measure each doorway at the floor, across the opening, and enter the total.
Several rooms
Each rectangular room has its own perimeter, and the runs add. A 14 × 12 ft room and a 10 × 8 ft room together run 88 ft, the sum of 52 ft and 36 ft.
An L-shaped room
Do not add the perimeters of the two rectangles an L is made of: the edge where they join is not a wall. Take an L made of a 12 × 12 ft part and an 8 × 7 ft part. Added as two rooms, the planner gives 78 ft, which counts the shared 7 ft edge twice. The L’s actual walls run 64 ft, which is the perimeter of the 20 × 12 ft rectangle around it. For an L-shaped room that is a handy check; for a U or any room with more notches, measure the walls one by one.
This example assumes
- All rooms here are rectangles, and every wall is covered
- The L-shaped example is a 12 × 12 ft part joined to an 8 × 7 ft part along a 7 ft edge
Then convert to pieces
Linear feet are only half the purchase: the run is divided by the length of the pieces you buy, with an allowance, and rounded up. That step is in how much baseboard you need. The general measuring habits for rooms are in how to measure a room.
What changes the estimate?
- Whether the trim stops at doorways, which depends on the trim
- Rooms that are not plain rectangles
- Walls the trim will not run along, such as a built-in
- The allowance and piece length, which come after the measuring