Follow these steps to determine how many rolls of wallcovering you'll need.
1. Calculate the wall space to be covered in square feet. Measure a wall from ceiling to floor and horizontally from corner to corner. Multiply those two figures. Repeat for remaining walls. Add the totals.
2. If you're covering a ceiling, calculate the square footage by multiplying the width of the floor by the length.
3. Divide each figure by 25 -- the average square footage in a standard single roll of wallpaper.
4. Subtract from the total one-half single roll for each window and door. The resulting figure is the final number of single rolls needed. Always round fractions to the next highest whole number. If your wallpaper comes in double rolls (most residential wallpapers do), divide this figure by 2.