Wallpaper Calculator

Background.

Divide 348 square feet of wall by the 56 square feet that a 20.5-inch by 33-foot roll covers and you get just over six, so 7 rolls. Hang that paper, with a 21-inch pattern repeat, on 8-foot walls and you will need 10. The label is not lying about its coverage. Wallpaper goes up in vertical strips, each a full wall height long, and a roll yields only as many whole strips as fit in its length; whatever is left at the end is too short to make another.

A pattern repeat makes those leftovers bigger. Each strip has to begin at the same point in the design so the motif lines up across the seams, which means every strip is cut to a whole number of repeats. With a 21-inch repeat an 8-foot wall takes five repeats, or 8.75 feet a strip, and a 33-foot roll gives three strips with 6.75 feet to spare. The same roll in a plain design gives four strips, and the room needs 8 rolls instead of 10.

So the count here works strip by strip, the way a paperhanger plans a room: how many strips span the walls, how long each one is cut, how many come out of a roll, and how many rolls that adds up to. Doors and windows are recorded but do not shrink the order, and an optional waste allowance covers damaged strips or a spare roll. Order the whole quantity at once. Rolls from different print runs can differ in shade, and a roll bought later to finish the last wall may not match the first.

What is wallpaper calculator?

Wallpaper is estimated in drops: single vertical strips cut from the roll, each long enough to run from the ceiling line down to the top of the baseboard. Roll width decides how many drops it takes to get across the walls, and roll length decides how many drops one roll can supply. The pattern repeat is the vertical distance after which the design starts over, printed on the label in inches or centimetres. How neighbouring strips line up is called the match. In a straight match the motif sits at the same height on every strip. In a drop match, usually a half-drop, every other strip is shifted down by part of the repeat. In a random or free match, such as stripes, plain colours and many textures, any strip can hang beside any other. Some manufacturers ask for random-match textures to be reverse hung, every other strip turned upside down, to even out shading from one edge of the roll to the other.

How to use this calculator.

1. 01Measure across every wall you are papering and add the widths for Total wall width, in feet. Measure straight past doors and windows; a 12 by 12 foot room has 48 feet of wall.
2. 02Enter Wall height in feet, from the top of the baseboard to the ceiling or crown molding. The figure is used exactly as entered, so if you want trimming allowance add it here: 8 feet plus 2 inches at each end is 8.33.
3. 03Copy Roll width in inches and Roll length in feet from the label of the roll you will actually buy. For a metric label, divide centimetres by 2.54 and metres by 0.3048: a roll of 53 cm by 10.05 m is 20.87 inches by 32.97 feet.
4. 04Enter Pattern repeat in inches from the label, or 0 for a plain, striped or random-match paper.
5. 05Opening area (doors and windows) is optional and only changes the net wall area. Waste allowance covers miscut or damaged strips and a spare roll; leave it at 0 for the bare strip count.
6. 06Enter Price per roll for the same unit whose length you entered, then order the Rolls to buy figure, checking that every roll carries the same batch number.

The formula.

Four quantities lead to the roll count. The number of strips is N = ⌈W ÷ (Rw ÷ 12)⌉: total wall width W in feet divided by the roll width Rw converted from inches to feet, rounded up, because the last narrow gap still takes a whole strip. The drop length is D = ⌈H ÷ (r ÷ 12)⌉ × (r ÷ 12), the wall height H rounded up to a whole number of repeats r; with a repeat of 0, D is simply H. Strips per roll is P = ⌊Rl ÷ D⌋, the roll length divided by the drop and rounded down, since a strip that falls short of the floor covers nothing. Rolls to buy are ⌈N ÷ P⌉, then multiplied by 1 plus the waste allowance and rounded up again. Cost is rolls times the price per roll. Gross wall area (W × H) and net area (gross minus openings, never below zero) are reported but take no part in the roll count.

Because P is rounded down, the result moves in steps rather than smoothly. A plain paper on a 33-foot roll gives four strips to any wall up to 8.25 feet high and only three above it, so on 48 feet of wall an 8.25-foot height needs 8 rolls and an 8.3-foot height needs 10.

The drop rule is the straight-match case. A drop match can use more length, because alternate strips start part way down the repeat, so add some waste allowance for one. The whole run of wall is divided once, as if the strips continued unbroken around the room; in practice the strip at each inside corner is split, with a small overlap, and the remainder starts the next wall, and Maharam's instructions ask for at least 6 inches wrapped around an outside corner. Those overlaps are not counted. All drops are assumed to be the same length, and if a single drop is longer than the roll, the calculator refuses with an error on the roll length, since that roll cannot supply even one strip.

A worked example.

Frequently asked questions.

References& sources.

1. [1]ASTM International (2024). "ASTM F793/F793M: Standard Classification of Wall Coverings by Use Characteristics." ASTM.
2. [2]Maharam (2024). "Wallcovering Installation Instructions." Maharam.
3. [3]National Institute of Standards and Technology (2026). "NIST Handbook 133, Appendix E: General Tables of Units of Measurement." U.S. Department of Commerce.
4. [4]National Institute of Standards and Technology (2008). "Guide for the Use of the International System of Units (SI), NIST Special Publication 811." U.S. Department of Commerce.
5. [5]Bureau International des Poids et Mesures (2019). "The International System of Units (SI Brochure), 9th edition." BIPM.