How to calculate wallpaper
Wall area is length × height, less standard openings. Strip count is based on the equivalent net wall width divided by roll width. The number of full-height strips obtainable from a roll depends on wall height and pattern repeat.
Wallpaper formula
Strips needed = equivalent net wall width ÷ roll width. When a pattern repeat is entered, each strip's cut length rounds up to the next full repeat. Rolls equal strips needed ÷ strips per roll, rounded up.
Worked example
A room with a 44-foot perimeter and 8-foot walls has 352 square feet before openings. One standard door and two windows reduce the planning area to 301 square feet. A 20.5-inch × 33-foot roll yields four 8-foot strips.
Practical tips
- Confirm whether a product is sold as a single roll or packaged as a double roll.
- Buy all rolls from the same dye lot.
- Large patterns, half-drop matches, damaged lengths, and complicated openings can increase waste.
Assumptions and limitations
Standard doors are treated as 21 ft² and windows as 15 ft². Openings are converted to equivalent wall width; this simplified method may reuse offcuts more efficiently than the actual layout. The recommendation adds one roll for matching and repairs.
Frequently asked questions
Why does pattern repeat increase the estimate?
Each strip must begin at a matching point, so usable strip length rounds up and fewer strips may fit on each roll.
Should I subtract every opening?
Usually not. Small openings still require full strips and careful matching. Subtract only substantial standard openings and keep an allowance.