Paper smoothly.

How to measure a wall for wallpaper

Every wallpaper estimate starts the same way: measure the walls, subtract the big openings, and you have the area to cover. Add up the width of every wall you're papering to get the perimeter, then multiply by the ceiling height. A 12 by 14 room has a perimeter of 52 feet, and at a 9-foot ceiling that's 468 square feet of gross wall. If you're only papering an accent wall, just use that one wall's width times the height.

Then subtract the openings, but only the large ones. A standard door is about 21 square feet and a typical window about 15, so a room with one of each drops from 468 to 432 square feet. Small windows and anything you'll paper around tightly aren't worth subtracting, because the offcuts rarely reuse cleanly, and the leftover margin protects you against a miscut. That net area is what the calculator above needs, along with the roll size and pattern repeat, to give you a roll count.

Wallpaper roll sizes: single, double, and metric

The most confusing thing about buying wallpaper is that it's priced and sold in a unit that isn't the unit that hangs on your wall. In the US, wallpaper is almost always sold as a double roll: two single rolls' worth of paper on one bolt. A double roll is the standard purchase unit even though the price tag sometimes quotes the single-roll figure, which trips up first-time buyers into thinking they need twice as many as they do. A US double roll holds about 72 square feet on the bolt and covers roughly 60 after you trim the top and bottom of each strip.

European and metric rolls run narrower and longer, so their coverage is different, and grasscloth and wide-format papers differ again. The single rule that survives all of it: buy by usable square feet, not by the number on the label. The calculator's roll-size selector is built around usable coverage precisely so the roll count reflects what actually reaches the wall.

Pattern repeat is the variable that ruins every estimate

Roll coverage tells you how much paper is on the bolt. Pattern repeat tells you how much of it you'll actually use, and it's the number that separates a clean estimate from an ugly surprise. The repeat is the vertical distance before the design starts over. To align the pattern across two adjacent strips, you often have to cut each strip longer than the wall height and discard the difference, and that discard can be as much as one full repeat per strip.

Put numbers on it. A 21-inch repeat on paper for a 9-foot (108-inch) ceiling means each strip has to be cut to the next multiple of the repeat above the wall height. So instead of 108 inches per strip you cut to 126 inches, and 18 inches goes in the bin. On a room that needs 15 strips, that's over 22 feet of wallpaper wasted purely on pattern matching, which is often a full extra roll. The bigger the repeat, the more you lose, which is why a bold large-scale print always needs more rolls than a plain texture covering the identical wall.

What wallpaper costs

Material cost swings widely by type. Peel-and-stick is the budget, renter-friendly option and the easiest to hang. Standard vinyl and non-woven papers sit in the middle and cover most living spaces. Designer papers and natural grasscloth are where the price climbs, and grasscloth adds the complication that it has no repeat to match but shows seams and shading, so it's less forgiving to hang despite the simple math.

Prep the wall before the first strip

The measurement gets the rolls right, but the wall underneath decides whether they stay up. Wallpaper needs a smooth, clean, sealed surface, and the prep is where most bad results actually start, not the hanging. Bare new drywall has to be primed first, because the porous paper face grabs adhesive unevenly and, worse, bonds so hard that the wallpaper becomes nearly impossible to remove later without tearing the drywall face off with it. A coat of wallpaper primer (sometimes called sizing) seals the surface and gives a uniform grip.

Previously painted walls usually just need cleaning and a light scuff, though glossy paint should be dulled so the adhesive can bite. Existing wallpaper should come off entirely rather than getting papered over, since hanging new paper over old traps the seams and bubbles of the layer beneath and telegraphs them through. And any holes or dents should be filled and sanded flush first, because wallpaper highlights a bad surface rather than hiding it, especially in raking light. Skipping prep is the false economy that turns a clean roll count into a peeling, bubbled wall a month later.

Where wallpaper estimates go wrong

Ignoring the pattern repeat. The biggest and most expensive miss. Estimating from wall area alone, with no repeat waste, leaves you one or two rolls short on any patterned paper, and by the time you notice you're mid-project and the dye lot is gone. Always add the repeat.

Confusing single and double rolls. US wallpaper is sold in double rolls but sometimes priced by the single. Order "10 rolls" when you meant 10 double rolls and you might get half what you need, or double. Confirm the unit before you buy.

Buying across dye lots. Splitting an order across two batches, or going back for one more later, risks a visible color shift on the wall. One lot, bought all at once, with the spare roll included.

Subtracting every little opening. Taking out small windows and outlets to save paper backfires, because those offcuts almost never reuse and the missing margin leaves you short on the next miscut. Subtract only doors and large windows.

If you're still weighing wallpaper against a simpler finish, the paint calculator uses the same wall measurements you took here, and paint runs three to five times cheaper in materials and far faster to apply. Most homeowners wallpaper one or two feature rooms and paint the rest. If you're papering over new drywall, the drywall calculator covers the surface underneath.