To calculate how many rolls of wallpaper will be required use this simple calculation:
1. Measure the perimeter of the room and then divide this figure by the width of the roll (X).
2. Divide the length of the roll by the drop + 10cm (Y).
3. Divide X by Y to give the number of rolls needed.
Example, say the perimeter of the room (including windows/doors) is 14m and the width of the roll is 0.6m then X = 24 (rounded up).
Another example say the roll length is 11m and the drop (+10cm) is 2.5 so Y = 4.4
Dividing X by Y gives us 24 ÷ 4.4 = 5.45, so we need 6 rolls to complete the project.