Wallpaper Roll Calculator

Wallpaper estimating goes wrong in two predictable ways. People forget that strips have to start from a level top edge, so any pattern repeat over a few inches forces extra waste. And people forget that you cannot cut around windows efficiently, because the off-cuts almost never line up with the next strip.

The basic math: figure how many strips of paper your walls need, then how many strips you get out of one roll, then divide.

strips_needed = wall_perimeter / roll_width strips_per_roll = floor(roll_length / strip_length)

Strip length is wall height plus the pattern repeat, which is the killer for big florals. A wallpaper with a 24-inch repeat means each strip is up to 24 inches longer than the wall is tall. On a standard 8-foot wall that is 25 percent extra paper on every single strip.

A worked example. Bedroom is 12 ft × 14 ft, 8 ft ceiling, two windows totalling 35 sq ft, one door 21 sq ft. Wallpaper roll is the standard American size: 27 inches wide, 27 ft long. Pattern repeat is 18 inches.

• Perimeter: 2 × (12 + 14) = 52 ft
• Strips needed: 52 × 12 / 27 = 23.1, round up to 24 strips
• Each strip: 8 ft + 18 in = 9.5 ft long
• Strips per roll: floor(27 / 9.5) = 2 strips
• Rolls before subtracting openings: 24 / 2 = 12 rolls
• Subtract one full roll for the windows-plus-door area: 11 rolls
• Add 10 percent for matching errors and short cuts: round up to 13 rolls

If you sell off the leftover at the end, fine. But under-buying by one roll on a discontinued pattern is the kind of mistake people remember for years. Add an extra roll to whatever the math says when the paper is bespoke or imported. It is cheap insurance on an expensive job, and you cannot go back for the same dye lot six months later.

European rolls are 20.5 inches wide and 33 ft long, which works out to 56 sq ft against 61 for the American roll. Close on area, quite different in shape, and that shape is what changes your strip count. Enter the roll you are actually buying rather than assuming the two are interchangeable.

Random match patterns, where the design has no horizontal alignment, waste less. Drop match patterns waste more, because every other strip is offset by half the repeat distance. The calculator below uses the conservative straight-match assumption, which over-estimates slightly for random match and is roughly right for drop match.