How to calculate wallpaper rolls
Work out how many strips (drops) fit across your walls: total width divided by roll width. Then see how many strips you can cut from one roll: roll length divided by wall height plus the pattern repeat and a trim allowance. Divide the strips by strips per roll.
Pattern repeat
A large pattern repeat means more waste, because each strip must start at the same point in the pattern. The repeat is printed on the roll label, usually in cm and inches.
Always buy one extra roll from the same batch. Different batches can vary slightly in colour.