Enter your room size, wall height, roll size and pattern repeat, and get how many rolls of wallpaper to buy — counted strip by strip, the way a pro estimates it.
The reliable way to estimate wallpaper isn't by area — it's strip by strip. First measure the perimeter (the distance all the way around the room) and the wall height. Divide the perimeter by the roll's width to get how many vertical strips, or "drops," you need to go around the room. Then work out how many full drops you can cut from a single roll: the roll's length divided by the height of one drop — and each drop needs the wall height plus a few inches of trim plus the pattern repeat. Divide the strips you need by the strips per roll, round up, and add a spare. This calculator runs that whole method for you.
On a patterned paper every strip has to start at the same point in the design so the seams match — which means trimming off part of the top of each strip, sometimes almost a whole repeat. A bigger repeat means fewer usable full-length drops per roll and more rolls overall. For a plain paper or a "free match" (random) pattern, enter 0 for the repeat and you'll waste almost nothing. Your paper's repeat is printed on the label, in inches or centimeters.
Wallpaper is often priced by the single roll but sold as a double roll — one longer bolt that gives you more usable strips with less waste. Pick the roll type that matches your paper, or check its label for the exact length and width. Always buy at least one extra roll from the same batch: dye lots vary between print runs, and a mid-project mistake is much cheaper to fix from a spare than from a new, slightly-different roll.
This is a planning aid. It counts full-height drops around the room and adds trim and pattern-repeat waste, then a spare roll — the same method a professional paperhanger uses. It does not subtract for doors or windows (you hang full drops past them and trim), so for a room with a very large opening you may need a roll or two fewer. Always confirm your roll's real length, width and repeat from the label before buying.