Question: how to calculate how much wallpaper you will need?
Answer: For example, if your total surface area is 480 square feet (45 m2) and each roll gives you 25 square feet (2.3 m2) of usable wallpaper, then 480/25 = 19.2.
Round the answer up to the nearest number. ... 
Wallpaper is sold in single and double rolls.