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 — 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 — for a standard 8-foot wall, that is 25 percent extra paper per 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. Two of three pros say to add an extra roll to whatever the math says when the wallpaper is bespoke or imported. The extra roll is cheap insurance on an expensive job.

European rolls are 20.5 inches wide and 33 ft long, by the way — about the same total square footage as American rolls but a different shape. If you mix imperial and metric numbers in the same calculation, you will be off by 30 percent and it will not be obvious where.

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