How to use the wallpaper calculator
- Enter the Total wall width (ft): every wall you will cover, added together. A 12 x 8 ft room is 40 ft, and a single feature wall is just that wall.
- Enter the Wall height (ft) from floor to ceiling, using the tallest point if the ceiling varies.
- Pick your Roll type from the label. A US double roll is 20.5 in x 33 ft. If yours differs, choose Custom roll size and fill in Roll width (inches) and Roll length (ft).
- Type the Pattern repeat (inches) from the label, or 0 for plain or random paper. If the label says drop match, set Pattern match to Drop (half-drop).
- Leave Doors and windows to skip at 0 for the safest order, then read the rolls needed.
How the rolls are worked out
The calculator uses the strip method from Family Handyman. Strips needed is the total wall width divided by the roll width, rounded up. Each strip is cut to the wall height plus 4 inches for trimming, rounded up to a whole pattern repeat when there is one (drop match adds half a repeat). Strips per roll is the roll length divided by that cut length, rounded down, because strips cannot be pieced. Rolls needed is strips divided by strips per roll, rounded up. If you skip doors and windows, each takes off 20 sq ft, the standard deduction in the Sherwin-Williams estimating steps, converted into whole strips.
Worked example with the default inputs
Walls totaling 40 ft wide and 8 ft high, on a double roll (20.5 in x 33 ft) with no repeat. The wall area is 320 sq ft. The width is 480 in, and 480 divided by 20.5 is 23.4, so you need 24 strips. Each strip is 96 + 4 = 100 in, or 8 ft 4 in, and a 396 in roll holds 3 of them. So you need 24 divided by 3 = 8 rolls, and the tool suggests ordering 9 with one spare. A 24 in straight-match repeat makes each strip 10 ft, which still fits 3 per roll, so the answer stays at 8 rolls.
Limits and edge cases
- US stores often price by the single roll but sell double rolls, so check the label for the real width and length. A single roll is about 28 sq ft and a double roll about 56 sq ft.
- Each strip must fit on one roll. If your wall is taller than a roll is long, the tool says so instead of guessing.
- Murals, grasscloth and borders have their own ordering rules, so confirm the quantity with the seller.
- Painting the other walls? Use the paint calculator, and the area converter if the label gives square meters.
Frequently asked questions
How many rolls of wallpaper do I need for a 12 x 12 room?
The walls total 48 ft. With 8 ft ceilings and double rolls (20.5 in x 33 ft), you need 29 strips, and each roll gives 3 strips, so 10 rolls. Order 11 to keep one spare.
What is a pattern repeat and how does it change the amount?
The pattern repeat is the vertical distance before the design starts over, printed on the label. Each strip is cut longer so the pattern lines up with the next one, so a bigger repeat wastes more paper and can lower the strips per roll.
Should I subtract doors and windows for wallpaper?
Family Handyman says not to leave them out, because you cut around them as you hang. Sherwin-Williams takes off 20 sq ft for each standard one. The calculator skips them by default for a safe order, and you can enter a count to take them off.
Why order an extra roll of wallpaper?
An extra roll covers mistakes and later repairs. Rolls are printed in batches that can differ slightly in color, so buy everything at once and check that the run numbers match.
Sources: Family Handyman, How to Calculate the Amount of Wallpaper You Need; Sherwin-Williams, How-To Estimate How Much Wallpaper You Need.