How it works
The calculator finds the room’s perimeter, subtracts doorways and gaps, adds your waste allowance and divides by the length of one piece.
Perimeter = 2 × (Length + Width) or entered directly
Run = Perimeter − Doorways and gaps
Run incl. waste = Run × (1 + Waste ÷ 100)
Pieces = ⌈ Run incl. waste ÷ Piece length ⌉
⌈ ⌉ means rounding up to the next whole piece. Rounding happens only at the end.
This is a length estimate. Every wall needs its own piece or pieces, and short offcuts can rarely be used, so a room with many short walls may need more pieces than shown – plan the cuts wall by wall if you want an exact count.
Worked example
Inputs
- Measure by
- Room length × width
- Room length
- 15 ft
- Room width
- 12 ft
- Doorways and gaps
- 3 ft
- Piece length
- 16 ft
- Waste allowance
- 0 %
Result
- Room perimeter
- 54 ft
- Baseboard run
- 51 ft
- Run incl. waste
- 51 ft
- Pieces
- 4
Common mistakes
- Forgetting to subtract doorways – or subtracting openings that do get trim, such as a closet with no door that is trimmed inside.
- Counting only total length. Offcuts from one wall are often too short for the next, so a room with many short walls needs more pieces than the length suggests.
- Leaving no allowance for corner cuts. Each inside and outside corner uses some length, and a bad miter means recutting.
- Mixing up nominal and actual piece length. Use the length printed on the label or product page.
Assumptions and limits
- In room mode, the room is a rectangle; the perimeter is 2 × (length + width). For other shapes, enter the perimeter.
- Doorways and gaps are subtracted as one total length.
- Pieces are counted from total length and rounded up to whole pieces. Individual cuts and joints are not planned.
- Shoe molding, quarter round, corner blocks, nails and adhesive are not included.
Frequently asked questions
Do I subtract door openings?
Yes, baseboard stops at the door casing, so subtract the width of each opening. Add up all the openings and enter the total under doorways and gaps.
How much extra baseboard should I buy?
It depends on the number of corners and how well offcuts fit the shorter walls. The safest check is to plan the pieces wall by wall against the piece length you can buy. The waste allowance here adds a percentage to the total run.
Can I use this for crown molding or shoe molding?
For the length, yes. Enter only the gaps where that molding actually stops – crown molding at the ceiling, for example, may run across door openings that baseboard has to skip.
Sources
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 2, 2026