Formula
Openings come off the wall before the rolls are rounded up:
rolls = ceil((wall area − openings) / 25)
Twenty-five square feet is a planning coverage for one US single roll, below the theoretical sheet, so a repeat and the trim have somewhere to go.
Assumptions
- The roll is a US single roll.
- Usable coverage is 25 square feet.
- Openings are not papered.
Worked example
A 96 square foot wall with 21 square feet of openings needs 3 rolls.
Input definitions
- Usable coverage
- The square feet you plan to get from one roll after matching a pattern and trimming.
- Openings
- Doors and windows subtracted from the wall.
Limitations
A double roll, a European roll, or a very large repeat can cover a different area. The label on the roll wins.
Questions
Why 25 and not the full roll?
A US single roll is larger on paper. Pattern match and trim use some of it, so 25 is the planning figure.
What is the 21 in the example?
A single 3 by 7 foot door. Add windows the same way.