Wallpaper Calculator

Estimate wallpaper for one rectangular wall

Enter wall dimensions, optional openings area, roll dimensions, and an extra allowance. The calculator divides adjusted net area by nominal roll coverage and rounds upward.

To estimate a whole room in one pass, enter the combined run of wall as the width, then subtract the total area of the doors and windows.

Formula

Gross area is wall width multiplied by wall height. Entered openings are subtracted, the extra allowance is applied to that net area, and the result is divided by nominal roll coverage, which is roll width in inches divided by twelve and multiplied by roll length. Any partial roll rounds up.

Area is not the same as usable drops

This is an area estimate, and area is an optimistic model for wallpaper. Paper hangs in full-height strips called drops, and the piece left at the end of a roll that is shorter than one drop cannot be used on that wall.

Count the drops to check the answer. Drops per roll is the roll length divided by the wall height, rounded down. Strips needed is the wall width divided by the roll width, rounded up. Divide strips by drops per roll and round up.

A 20-foot wall 9 feet high takes 12 strips from a 20.5-inch roll. A 16.5-foot roll yields one drop, so that wall needs 12 rolls, while the area method suggests 8 at the default 10% allowance — and 7 with no allowance at all. The mismatch is largest when the roll length is not close to a whole multiple of the wall height, and no percentage allowance removes it, because the loss is in whole drops rather than proportional to area.

Pattern matching changes usable coverage

Nominal roll area is not always usable wall coverage. Pattern repeat, drop match, trimming, damaged sections, wall shape, and strip placement can require more material.

Buy every roll for a wall from the same batch or dye lot, and buy enough in one order. Rolls printed in different lots can differ in shade enough to show as a band on the finished wall, so returning for one extra roll often means re-hanging the whole wall.

Check the manufacturer’s coverage and pattern instructions before buying. Enter actual packaged dimensions because “single roll” and “double roll” terminology can be inconsistent.