Wallpaper Calculator: How Many Rolls Do You Need?

Wallpaper Calculator

A wallpaper calculator is a tool that works out how many rolls of wallpaper a room needs. It uses the room's length, width, and height, minus the area of any windows and doors, then divides that wall area by the usable coverage of one roll.

How to calculate wallpaper rolls

Two steps make up the calculation. First, find the total wall area. Second, divide that area by how much wall one roll can actually cover, then round up.

Wall area formula

$\text{Wall Area} = \text{Perimeter} \times \text{Height} - \text{Window/Door Area}$

• Perimeter = 2 × (Length + Width) of the room, in feet
• Height = wall height, from floor to ceiling (or to wherever the wallpaper stops)
• Window/Door Area = the combined area of every window and door opening that will not be papered

The result can never be less than zero. If the window and door area is larger than the wall area (which should not normally happen), the calculator treats the wall area as zero.

Rolls-needed formula

$\text{Rolls Needed} = \left\lceil \frac{\text{Wall Area}}{\text{Roll Coverage}} \right\rceil$

The symbol ⌈ ⌉ means "round up to the next whole number," because a store will not sell part of a roll. Roll coverage is the usable area, in square feet, that one roll actually supplies once it has been cut into strips.

Why the roll coverage number matters

A roll's usable coverage is smaller than the raw amount of paper on it. Every strip gets cut to the room's wall height, and the leftover at the end of each strip becomes scrap. Sherwin-Williams states that a single roll contains 25 usable square feet, regardless of width. US wallpaper is priced in single rolls but sold in double rolls, so one double roll gives about 50 usable square feet. Patterned paper yields less, because more paper is trimmed away to line up the design.

This calculator defaults to 50 square feet of usable coverage per double roll. Dividing by the raw paper area on the label instead will under-order wallpaper.

Roll sizes

Roll sizes differ by region and by maker, and premium or specialty wallpapers often use non-standard sizes. The usable coverage, not just the raw roll size, is usually printed on the packaging or the product listing. Enter that number into the calculator's roll coverage field when it is available. The calculator works in feet and square feet, so a coverage listed in square meters must be converted first (1 m² ≈ 10.76 sq ft).

Worked example

A living room measures 12 feet by 15 feet, with 8-foot ceilings and 30 square feet of windows and doors combined.

1. Perimeter: 2 × (12 + 15) = 54 ft
2. Wall area: 54 × 8 − 30 = 432 − 30 = 402 sq ft
3. Rolls needed, at 50 sq ft usable coverage per roll: 402 ÷ 50 = 8.04, rounded up to 9 rolls

A second example: a 20 ft by 30 ft dining area with 10-foot ceilings and 120 square feet of windows and doors.

1. Perimeter: 2 × (20 + 30) = 100 ft
2. Wall area: 100 × 10 − 120 = 1000 − 120 = 880 sq ft
3. Rolls needed: 880 ÷ 50 = 17.6, rounded up to 18 rolls

Pattern matching and waste

Wallpaper with a repeating pattern needs extra material, because each new strip has to line up with the pattern on the strip beside it. The pattern repeat is the distance before the design starts again. It is printed on the back of sample books and on most rolls, and can range from 0 to 23 inches. The larger the repeat, the more paper gets trimmed off to make the match.

The calculator does not add a pattern allowance. To account for it, multiply the wall area by (1 + the extra-material percentage) before dividing by the roll coverage:

$\text{Adjusted Wall Area} = \text{Wall Area} \times (1 + \text{Pattern Match \%})$

The manufacturer's label or product listing is the best guide to the right percentage for a given repeat.

Wallpaper is printed in batches, and colors can vary slightly between batches. Checking that every roll has the same run or lot number avoids a visible mismatch. Buying one extra roll covers cutting mistakes and later repairs.

How to use the wallpaper calculator

1. Measure the room's length and width at floor level, and the wall height from floor to ceiling. If ceiling height varies, as it often does in older homes, measure in a few spots and use the highest value.
2. Measure each window and door opening (width × height, including the frame) and add them together.
3. Enter the length, width, height, and combined window/door area into the calculator.
4. Enter the roll's usable coverage, in square feet, if the packaging lists one, or leave the default of 50 square feet for a standard US double roll.
5. Read off the total wall area and the number of rolls needed. Add extra rolls for a patterned wallpaper or for future repairs, as described above.

Irregular rooms and sloped ceilings

For an L-shaped room or one with an alcove, split it into two or three rectangular sections. Calculate the wall area of each section the same way, then add the totals together.

For a sloped ceiling, such as in an attic, measure the wall height at its lowest and highest points and average the two: (Lowest + Highest) ÷ 2. Using that average height in the formula gives a reasonable estimate for most rooms. For a very steep slope, the triangular section at the top can be calculated separately using the triangle area formula, ½ × base × height, and added to the rectangular section below it.

Frequently asked questions

How accurate is a wallpaper calculator? For a simple rectangular room with accurate measurements, the formula is exact geometry, so the result is reliable. Accuracy drops for irregular room shapes, patterned wallpaper without a waste allowance, or rolls whose usable coverage differs from the default.

Should windows and doors be subtracted from the wall area? Yes. Subtracting them avoids paying for paper that would cover an opening rather than a wall, and it can reduce the roll count by one or more on a room with several windows.

What roll coverage should be entered if the packaging does not list a usable yield? Use 50 square feet for a standard US double roll. This figure already accounts for trim waste, unlike the raw paper area printed on the label.

How is wallpaper calculated for a sloped ceiling? Average the lowest and highest wall heights and use that average in the wall area formula. For ceilings with a large height difference, calculate the triangular top section separately and add it to the rectangular section.

Does peel-and-stick wallpaper use the same calculation? Not exactly. Peel-and-stick wallpaper is often sold in panels of a fixed size rather than continuous rolls. Divide the wall area by one panel's area instead of a roll's coverage, then round up.

How much extra wallpaper should be bought for repairs? One extra roll beyond the calculated amount is common practice. Wallpaper is printed in batches, so a roll bought later, even of the same pattern, may not match the original color exactly.

References

1. Sherwin-Williams. How much to buy? (wallpapering how-tos). How much wallpaper to buy — 25 usable square feet per single roll regardless of width, single-roll pricing with double-roll sales, pattern repeats from 0 to 23 inches, excluding windows and doors, color variation between print batches, and buying an extra roll.
2. National Institute of Standards and Technology. NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement. Handbook 44 Appendix C — 1 square meter = 10.763 91 square feet.