How to calculate baseboard
Baseboard runs around the room at floor level and stops at each door casing. So the amount you need is the room perimeter minus the width of the door openings, plus an allowance for miters and offcuts.
length = (2 × (L + W) − door widths) × (1 + waste %)
pieces = length ÷ piece length, rounded up
Worked example
A 14 × 12 ft bedroom has a perimeter of 52 ft. One 36 in door opening removes 3 ft, leaving 49 ft. Add 10 percent and you need 53.9 linear feet: four 16 ft pieces or seven 8 ft pieces. In metric, a 4 × 3.5 m room has a 15 m perimeter; a 900 mm doorway leaves 14.1 m, and with 10 percent extra you need 15.51 m, or five 3.6 m lengths.
Crown molding and other trim
Crown molding runs along the top of every wall without breaks for doors, so use the full perimeter: set door openings to 0. Crown also needs more waste because its compound miters are less forgiving. For the same 14 × 12 ft room with 15 percent extra, you need 59.8 linear feet, which is four 16 ft pieces.
| Trim | What to measure | Typical waste |
|---|---|---|
| Baseboard | Perimeter minus door openings | 10% |
| Shoe molding or quarter round | Same as baseboard | 10% |
| Crown molding | Full perimeter | 15% |
| Chair rail | Perimeter minus doors and any windows it meets | 10% |
| Door casing | About 17 ft per side for a standard door, both legs and the head | Buy as kits or full pieces |
These waste figures are rules of thumb. Rooms with many short walls, bay windows or outside corners use more.
Choosing piece length
- Longer pieces mean fewer joints. Try to cover each wall with one piece where you can; a 14 ft wall looks best with a single 16 ft board.
- Where you must join two pieces on a long wall, use a scarf joint (two 45° cuts that overlap) over a stud, not a square butt joint.
- Short pieces are easier to carry and fit in a car, but each joint costs a little extra length and time.
- Count the walls longer than your piece length. Each one needs at least one joint, which can mean an extra piece beyond the total-length estimate.
L-shaped and open-plan rooms
The length × width inputs assume a rectangle. For an L-shaped room, measure every wall and add them up; the total is the perimeter. Enter half of it as the length and 0 as the width, or split the room into rectangles and leave out the walls they share. In open-plan spaces, stop where the baseboard ends at a cabinet run, a fireplace or a stair.
Nails and supplies
A common rule of thumb is to pick finish nails long enough to pass through the trim and the drywall and reach about 1 in into the framing. For ½ in baseboard on ½ in drywall that means 2 in nails (½ + ½ + 1). Nail into the studs and the bottom plate, two nails at each stud for taller boards. You will also want wood glue for outside miters and scarf joints, wood filler for the nail holes, and paintable caulk for the gap along the top edge if the trim is painted.
Measuring tips
- Measure each wall at floor level, where baseboard sits, rather than taking the room size from a plan.
- Include closets if they get baseboard, and add short returns at built-ins or fireplace hearths.
- Install flooring before baseboard. The baseboard, or a shoe molding, covers the expansion gap that floating floors need at the walls.
- Buy the whole job from one batch so the profile and color match. Paint-grade trim can be primed before you cut it to save time.
Frequently asked questions
How much baseboard do I need for a 12 × 14 room?
The perimeter is 52 ft. Remove a 3 ft door opening and add 10 percent and you need about 53.9 linear feet, or four 16 ft pieces.
How many 16 ft pieces of baseboard for a 20 × 15 room?
The perimeter is 70 ft. With two 36 in doors removed it is 64 ft, and with 10 percent extra it is 70.4 ft, so buy five 16 ft pieces.
Do I subtract doors for crown molding?
No. Crown runs over door openings at the top of the wall, so measure the full perimeter and add about 15 percent for cuts.
How much extra baseboard should I buy?
About 10 percent for a simple room. Add more for rooms with many corners, short walls or bay windows.