How to use the baseboard calculator
- Enter the room length and width.
- Enter the number of door openings and their width.
- Enter the length of the pieces you will buy. 8, 12 and 16 ft are common.
- Keep about 10% extra for mitred corners and joins.
Measure each wall separately and write the lengths down before you add them up; Decoratoradvice finds that short runs behind doors are the ones most often missed.
Baseboard formula
Perimeter = 2 × (length + width)
Wall length to trim = perimeter − door openings
Baseboard = wall length × (1 + extra)
Pieces = baseboard ÷ piece length, rounded up
Worked example
A 14 × 12 ft bedroom with one 3 ft door, 12 ft pieces, 10% extra:
Perimeter: 2 × (14 + 12) = 52 ft
Minus the door: 49 ft
With 10% extra: 53.9 ft
53.9 ÷ 12 = 4.49, so 5 pieces
Choosing piece length
Longer pieces mean fewer joins on long walls, which look better once painted. A 14 ft wall can be done in one 16 ft piece but needs a join with 12 ft pieces. Short pieces are easier to carry and to fit in closets.
Tips
- List each wall with its length and buy pieces to cover the longest walls without joins.
- Paint or stain baseboard before installing it, then touch up nail holes. The paint calculator covers walls; trim usually needs a quart or two.
- Install baseboard after flooring so it covers the expansion gap the flooring calculator and carpet calculator floors need.
Common mistakes
- Forgetting closets. Their walls need trim too.
- Not subtracting doors. Openings need casing, not baseboard.
- No allowance for corners. Each outside and inside corner wastes a few inches.
Frequently asked questions
How much baseboard do I need for a 12 × 12 room?
The perimeter is 48 ft. With one 3 ft door, 45 ft, or 49.5 ft with 10% extra.
Do I subtract doorways?
Yes. Measure the width of each opening and subtract it.
How much extra trim should I buy?
About 10% covers mitred corners and the odd bad cut in an ordinary room.
What lengths does baseboard come in?
Commonly 8, 12 and 16 ft. Availability varies by profile and supplier.
Should baseboard go on before or after flooring?
After, in most cases, so it covers the edge of the floor and any expansion gap.
Do I need baseboard with tile floors?
Usually yes, or a tile base. The tile calculator counts floor and wall tile.
Key takeaways
- Baseboard = perimeter − door openings, plus about 10%.
- Divide by piece length and round up.
- Use long pieces on long walls to avoid joins.
- Fit baseboard after the flooring.