Wallpaper Calculator

Start by measuring the perimeter and the wall height, not the window openings. Wallpaper hangs in vertical strips from ceiling to floor, so the room footprint is what drives the roll count. Once you know how tall the strips run and how many strips wrap around the room, the door and window deductions are a small correction on top.

A standard US roll covers about 30 square feet of finished wall. That number sounds generous, but a repeating pattern throws a fair amount of paper away on matching seams, which is why the roll count always ends up a little higher than the raw wall area suggests.

Measure the perimeter first

Walk the tape around the room and add all four walls. For an average bedroom that lands around 40 feet of perimeter. Multiply by the wall height, usually 8 feet, and you have the gross wall area, roughly 320 square feet.

You do not need to measure every wall to the inch. Wallpaper strips run straight up and down, and corners, alcoves and half-walls add and subtract in ways that the waste factor already absorbs. The number that has to be right is the total perimeter, because every foot of it gets a strip.

Deduct doors and windows

Doors and windows are openings you will not paper, so pull them out of the gross area. Budget 15 square feet per door and 15 per window, which is a touch less generous than the paint figure because wallpaper rarely wraps onto the trim around them.

Take that 40 foot perimeter room. Two doors and two windows pull about 60 square feet out of the 320, leaving around 260 square feet of actual wall. Divide by the 30 square feet a roll covers, and the raw count lands around 9 rolls.

Pattern matching changes everything

This is where the math stops being simple. A plain texture or a small random pattern can be cut strip to strip with no alignment, and the 30 square foot figure holds. A pattern that repeats every 20 inches or more forces you to drop each strip until the flowers or stripes line up at the ceiling.

That dropped paper is waste you cannot avoid. The rule of thumb is to buy one extra roll whenever the pattern has an obvious repeat, and to buy every roll from the same dye lot. Two rolls of the same wallpaper name made on different days can carry a shade difference that is impossible to blend on a finished wall.

Roll sizes differ by origin

US rolls run about 21 inches wide and 16 and a half feet long, which works out near 30 square feet. European rolls are a different beast, often closer to 56 square feet per single roll, so a room that calls for 9 US rolls might only need 5 European ones.

Check the label on the specific product you buy. Designer lines and grasscloths sometimes come in shorter rolls, and guessing on the coverage is how you end up one roll short on the last wall.

Strip layout and the ceiling

Wallpaper strips run vertically, so the width of the roll sets how many strips wrap the room. A 21 inch wide roll means each strip covers just under 2 feet of wall, and corners never line up perfectly, which is another reason the waste factor exists.

If you have a chair rail, wainscoting or a wallpapered ceiling, those are separate areas measured on their own. Most rooms stop the paper at the ceiling line and paint above it, which keeps the strip count simple.

The final order

That 40 foot perimeter room with 8 foot walls, two doors and two windows needs about 9 rolls on the raw area. Add the single extra roll for pattern matching, and you are buying 10. Buy them all at once, in one trip, from one dye lot.

Leftover rolls are not a failure. A spare roll stored in a dry closet becomes the fix when a movers scratch, a nail hole or a toddler’s doodle needs a seamless patch years from now.

See also the paint calculator for the ceiling and trim that frame the paper, and the drywall calculator for the wall underneath.

A 40 foot perimeter with 8 foot walls, two doors and two windows needs about 9 rolls.