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.
If you are covering a ceiling, calculate the square footage by multiplying the width of the floor by the length.
Divide each figure by 50 — the average square footage in a standard single roll of wallpaper.
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.