Wallpaper Calculator

A wallpaper calculator returns the double rolls to buy for a room. It counts the strips needed around the perimeter. It then works out how many strips one roll yields once each strip is cut to wall height plus one pattern repeat. Finally, it adds waste and rounds up to whole rolls.

Last reviewed September 2026Method & sources Report an error

Not to scale.

Strips Needed

Includes a 10% waste allowance.

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Wallpaper8 double rolls26 strips at 4 per roll.

Breakdown
Strips Needed	26
Usable Strips per Double Roll	4
Double Rolls to Buy	8
Estimated Cost

How to Calculate Wallpaper

Wallpaper is bought and hung by the strip, not by a flat area conversion, which is why a pattern repeat changes the roll count so much more than a simple square-footage estimate would suggest. The room's perimeter divided by the roll's width gives the number of strips needed to go around the room. Each strip is cut to the wall height *plus one full pattern repeat*, since the design has to line up with the strip next to it. That extra length gets trimmed off during hanging but has to be on the cut. Dividing the roll's total length by that cut length (rounded down, since a partial strip isn't usable) gives how many strips one bolt yields. Dividing the total strips needed by that figure gives the raw roll count. A waste allowance is added on top for mismeasure and pattern-matching mistakes. The standard double-roll bolt dimensions used here (20.5 in. × 33 ft, or 27 in. × 27 ft for wide-format papers) are the sizes used across major US wallcovering manufacturers.

Example: 12 ft × 10 ft room, 8 ft walls, standard 20.5 in. rolls, 10% waste

A 12 ft × 10 ft room, 8 ft walls, standard 20.5 in. rolls, 10% waste: With a 12 in. pattern repeat: 1. Perimeter: 2 × (12 + 10) = 44 ft. Roll width: 20.5 ÷ 12 = 1.708 ft 2. Strips needed: 44 ÷ 1.708 = 25.76, rounded up to 26 strips 3. Cut length per strip: 8 + (12 ÷ 12) = 9 ft 4. Strips per double roll (33 ft long): floor(33 ÷ 9) = 3 strips 5. Raw rolls: 26 ÷ 3 = 8.67. With 10% waste: 8.67 × 1.10 = 9.53, rounded up to 10 double rolls The same room with no pattern repeat (plain paper): Cut length is just 8 ft, so one roll yields floor(33 ÷ 8) = 4 strips. Raw rolls: 26 ÷ 4 = 6.5, ×1.10 = 7.15, rounded up to 8 double rolls. Same room, same rolls, but the 12 in. repeat needs 2 more double rolls than plain paper. That gap is exactly what a flat area-based estimate misses.

Wallpaper: Compare Scenarios

Scenario	Strips Needed	Usable Strips per Double Roll	Double Rolls to Buy
Small (8×8 ft powder room)	19	4	6
Medium (12×10 ft bedroom)	26	4	8
Large (16×14 ft living room)	36	4	10

What Is Wallpaper?

A wallpaper calculator converts a room's dimensions, roll size, and pattern repeat into the number of double rolls needed. It accounts for the fact that a patterned paper uses noticeably more material than a plain one. Every strip needs extra length cut in to keep the design aligned with its neighbor.

Wallpaper: Pros and Cons

Pros

Models wallpaper the way it's actually bought and hung, by the strip and the bolt, instead of a flat square-footage conversion that ignores pattern repeat entirely
Shows the real cost of a large pattern repeat directly in the roll count, which is the single biggest source of under-ordering on a patterned paper
Supports both standard and wide-format roll dimensions used across major US wallcovering manufacturers

Cons

Doesn't subtract door and window openings from the strip count. Professional estimators generally don't credit that savings either, since the cut-off pieces above and below an opening usually can't be reused elsewhere without breaking the pattern match
Assumes a rectangular room with one pattern repeat value throughout. A room with a chair rail, an accent wall only, or multiple wallpaper patterns needs each section calculated separately
A drop-match pattern (where alternating strips shift by half a repeat) can need slightly more waste than this calculator's straight-match assumption. Increase the waste allowance for a drop-match paper

Wallpaper: What a Pro Checks

Buy every roll from the same dye lot up front. Wallpaper is dye-lotted, so a roll ordered later to cover a shortfall may not match the color of rolls from an earlier production run.
Increase the waste allowance a few points above the default for a drop-match pattern. Alternating strips shift by a fraction of the repeat, which wastes more paper than a straight match.
Don't count on saving paper around doors and windows. The cut-off pieces above and below an opening usually can't be reused elsewhere without breaking the pattern match at the seam.

Frequently Asked Questions

How much does pattern repeat affect how much wallpaper I need?

Significantly. In the worked example above, adding a 12 in. pattern repeat to an 8 ft wall increases the double rolls needed from 8 to 10, a 25% jump. That jump comes purely from the extra length each strip needs cut in to keep the pattern aligned. Larger repeats (18 in. or more) waste even more.

What size is a double roll of wallpaper?

The most common US format is 20.5 in. wide by 33 ft long (about 56 sq ft), though some wide-format papers use 27 in. by 27 ft rolls instead. Despite the name, a "double roll" is typically sold as one continuous bolt of that length, not two separate rolls. The name refers to it being double the length of an older single-roll unit.

Why doesn't this calculator subtract doors and windows?

The leftover pieces above and below a door or window usually can't be reused on another wall without breaking the pattern match at the seam. Professional wallpaper estimators typically don't credit that area as savings, so this calculator's strip-based approach already reflects that conservative, standard trade practice.

What is a pattern repeat?

A pattern repeat is the vertical distance before a wallpaper's design repeats itself. A paper with no visible repeat (a plain color, a small random texture) has a repeat of 0, while a large floral or geometric print might repeat every 18-24 in. or more. The repeat distance is listed on the wallpaper's packaging or product page. Enter 0 if the pattern has no visible repeat.

What's the difference between straight match and drop match?

In a straight match, the pattern lines up horizontally straight across from one strip to the next. In a drop match, alternating strips shift down by half (or some fraction) of the repeat, so the pattern steps diagonally. This typically wastes a bit more paper than a straight match, since usable cut lengths land differently. If your paper is drop-match, increase the waste allowance a few percentage points beyond the default.

Should I round up or order exactly the calculated amount?

Round up, and consider one extra roll beyond this calculator's result for a large room or an important wall. Wallpaper is dye-lotted, meaning a roll purchased later to finish a shortfall may not match the color of rolls from an earlier production run exactly. Buying enough from the same dye lot up front avoids that risk entirely.

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