Wallpaper Measurement Guide
Width and height
Measure each wall you will paper. Do not measure only one wall and multiply, and do not rely on a single perimeter if the walls are different widths. A strip stops at the corner.
Width is the distance across the wall at the height where you will hang the paper. Height is the tallest distance from the line where the paper starts at the top to the line where it ends. If there is a baseboard and you will stop on it, stop the tape there. Measure the height in more than one place and use the largest figure.
Write feet and inches as you read them. 8 feet 6 inches and 8.5 feet are the same height. A room that looks square often is not, so measure all four walls.
Doors and windows
Measure the opening you will not paper: the width and the height of the hole. Add each door and each window on the wall it sits on.
Those sizes are subtracted from the wall area. They do not, by themselves, reduce the number of rolls. The drop is still cut to the full height, and you cut the door or window out of that strip. The piece above a door is rarely a full drop you can move to another wall, especially once a pattern has to match.
If an opening runs the full height you are papering, such as a glass door from the ceiling line to the base, enter that full height. The calculator removes one drop for each complete roll width inside that opening. Each opening is counted on its own, so two narrow openings are not added into one drop. If one opening is at least as wide as the wall, that wall needs no drops. A leftover strip narrower than the roll still needs a drop. The reduction assumes the opening lines up with the drops. If it crosses a seam, you may still need the strips on both sides.
The areas are assumed not to overlap. If two openings cover the same spot, the area will be counted twice until it is limited to the wall.
Pattern repeats
The repeat is the distance down the roll from one point in the design to the same point again. Random match, including many stripes and textures, does not need that distance. The drop is the wall height plus trim.
Straight match means every strip shows the same part of the design at the ceiling. The cut is the wall height plus trim, rounded up to the next whole repeat. If the height plus trim is already a whole number of repeats, nothing extra is added.
Drop match here means a half drop, which is the usual meaning: every other strip starts halfway through the repeat. The halfway distance is skipped on the roll between cuts. It is not pasted on the wall. A multiple drop, which takes four or more strips before the design repeats, is not calculated. If the label says that, ask the seller to check the quantity.
The first drop on a new roll is assumed to start where you choose to cut. A hanger who shifts the motif down from the ceiling can use up to one extra repeat on every drop. The trim box is the place to allow for that if you already know you will.
Roll dimensions
Read the width and the length on the roll label or the product page for the paper you are buying. This calculator does not assume one size, because there isn’t one.
The Wallcoverings Association says wallcoverings are made in different widths because mills use different equipment. It describes metric, or Euro, single rolls as about 27.5 to 29 square feet and double rolls as about 56 to 58 square feet. It describes older American single rolls as about 36 square feet and double rolls as about 72, and it says those American single rolls are being phased out. Those are area ranges, not one width and one length. The same page says contract wallcovering is often 48 or 54 inches wide and is sold by the lineal yard. Pages read 3 November 2026: Understanding Wallcoverings and Packaging and Sizes.
Retail guides often describe a residential double roll as about 20.5 to 21 inches wide and 33 feet long, sold as one continuous bolt. That is a common description, not a rule. The example buttons fill those two widths so you can try the math. Replace them with the label before you order.
A price “per single roll” can mean half of the bolt that arrives. The association notes that paper is often priced by the single roll and packaged as a double or triple roll. Confirm what one unit is before you compare a roll count with a cart quantity.
Examples
These use a roll 20.5 inches wide and 33 feet long, which is 396 inches, and 4 inches of trim, unless the example says otherwise.
One 12 by 8 foot wall, no pattern
The wall is 144 inches wide. 144 ÷ 20.5 is 7.02, so 8 drops. Each drop is 96 + 4 = 100 inches. 396 ÷ 100 is 3.96, so 3 drops per roll. 8 ÷ 3 rounds up to 3 rolls. The wall is 96 square feet. The roll’s label area is 56.375 square feet. Three rolls hold 169.125 square feet of paper before cutting, because the leftovers are not full drops.
The same wall with a door and a window
A door 36 by 80 inches is 20 square feet. A window 30 by 48 inches is 10 square feet. Net area is 66 square feet. Neither opening is the full 96 inches tall, so the roll count stays 3.
Straight match, 21 inch repeat
100 inches of height and trim need 5 repeats: 105 inches, which is 8 feet 9 inches. Five inches are rounding on each of 8 drops, 40 inches in all. Three drops of 105 inches still fit on the 396 inch roll, so the wall is still 3 rolls.
Why a half drop can cost more
On that same 12 by 8 foot wall, the half-drop skips still fit in 3 rolls: 63 inches are skipped to reach the halfway point, and 285 inches are left at the ends of the rolls. Shorten the roll to 220 inches and the same 4 drops take 2 rolls with a straight match and 4 rolls with a half drop, because the halfway skip no longer fits beside the cuts.
Wall by wall, not one perimeter
Four walls, 5 feet, 4 feet, 5 feet, and 4 feet wide, on a 21 inch roll, are 12 drops. The same lengths as one 18 foot run are 11 drops. The extra drop is the rounding on each wall.
Questions
How many rolls of wallpaper do I need?
Count full-height drops, then see how many of those cuts fit on a roll. Divide each wall’s width by the roll width and round up. Add your trim allowance. For a pattern, round that length up to a whole repeat. Divide the roll length by the cut length and round down. Divide the drops by that number and round up to whole rolls. Square feet alone usually come out short because the end of a roll is often too short for another drop.
Should I subtract doors and windows?
Subtract them from the area so you can see the net wall. A normal door or window does not lower the roll count, because each strip is still cut from the ceiling to the base and the hole is cut out of it. An opening as tall as the wall removes one drop for each complete roll width inside that opening. Each opening is counted on its own. If one opening is at least as wide as the wall, that wall needs no drops.
What is a wallpaper pattern repeat?
The pattern repeat is the vertical distance from one point in the design to the next point where that same part of the design appears. It is printed on the roll label. A straight match starts every drop at the same place in that distance. A half drop starts every other drop halfway through it.
What size is a roll of wallpaper?
There is no single US roll size. The Wallcoverings Association says mills use different widths and that a metric double roll is about 56 to 58 square feet, while older American double rolls were about 72 square feet. Retailers often describe a residential double roll as about 20.5 to 21 inches wide by 33 feet long. Use the width and length on your label.
How much extra wallpaper should I buy?
There is no fixed percent that fits every room. Pattern, ceiling height, and roll length change the waste, and this calculator counts that waste from the cuts. You can add an extra percent or spare rolls on top. A spare roll from the same dye lot is the practical reserve for a mistake or a later repair.