How to measure for wallpaper comes down to two numbers: how far the paper has to run around the room, and how tall the wall is. Everything else on a wallpaper order comes out of those, and the surprising part is what you leave in rather than what you take out. You measure straight past the doors and the windows.
Measure the run, not the room
Run a tape along the floor from corner to corner and write down each wall. Do not measure at the ceiling: floors and ceilings are rarely parallel in a real house, and the floor is the line the first strip is plumbed against anyway.
Then measure the height in three or four places across the room and keep the largest. A floor that falls half an inch across a room is ordinary, and a strip cut to the shortest drop is a strip you throw away.
That is the whole survey. Square footage is not a measurement you need to take, because paper is hung in full width strips and a strip is either there or it is not. Working in square feet is how a room that needs twelve rolls gets ordered as ten.
Measure straight past the doors and the windows
This is the opposite of what you do for paint, and it catches almost everybody. A strip of paper still has to be hung above a door and above and below a window, and it still has to be cut from a full length piece to get there. The opening removes a bit of the strip. It does not remove the strip.
Take a 12 by 14 foot room with nine foot ceilings, one door and two windows. Deduct them as area and you take 51 square feet off 468, which is 11 percent and feels like a roll saved. Deduct them as strips and you save nothing at all, because the run around the room has not changed by an inch.
The exception is an opening wide enough to swallow whole strips: a patio door, a picture window, a wall of glass. Take those out in whole strip widths and leave everything else in.
Corners are where the paper goes
Here is the measurement that actually costs money. Every internal corner ends a strip and starts a new one, because no room is square enough to carry a strip round a corner and still be plumb on the far side. So the part strip at the end of each wall is a whole strip you have paid for.
Measure the same 12 by 14 room as one perimeter of 52 feet and, on 20.5 inch paper, it comes to 31 strips and 11 rolls. Measure it as four walls and add them up and it is eight, eight, nine and nine: 34 strips, and 12 rolls. Same room, same paper, one roll apart, and the roll is the one you find out about on the last wall.
So write down each wall separately and keep them separate. It is one extra line in a notebook and it is the difference between finishing the room and driving back to the shop.
The walls that are not flat
A chimney breast is three walls, not one: the face and both returns, each measured and rounded on its own. An alcove beside it is another three. This is where a perimeter figure goes furthest wrong, because a room with a chimney breast has ten internal corners rather than four.
A sloped ceiling or a stairwell is measured at its longest drop, and that figure governs every strip on the wall, since you cannot cut a strip to a length you have not bought. A stairwell wall running from the upstairs landing to the hall floor can easily be 14 or 15 feet, which changes how many strips come off a roll for that wall and often for that wall alone.
Add the trim before you cut anything
Every strip is hung long and trimmed at both ends, top and bottom, so the cut length is the wall height plus a few inches. Two inches at each end is normal and four is safer on an older house where the ceiling wanders.
That allowance is not the same thing as the pattern repeat, which rounds the cut up again to the next whole repeat and is the other half of the ordering problem. The calculator handles both, but the trim is the number you have to decide, because it depends on your walls rather than on the paper.
Before you order: how to measure for wallpaper in short
Check what a roll actually is. American paper is usually sold as a double roll, so the price you see may be for half of what arrives, and entering the wrong one is the single most common mistake in a wallpaper order.
Then buy the whole job at once and check the batch or shade number is the same on every roll. Wallpaper is printed in runs and the runs do not match exactly. A roll bought a month later is a roll that will show, and it will show most on the wall you notice from the doorway.
Keep the spare rather than returning it. A torn strip in year three is a one strip repair if you have a match and a redecoration if you do not.
Run your measurements, one wall at a time
Frequently asked
Run a tape along the floor and write down each wall separately, then measure the height in three or four places and keep the largest. Keep the walls apart rather than adding them into one perimeter: every internal corner ends a strip, so a 12 by 14 room comes to 34 strips wall by wall against 31 as a perimeter.
No. A strip still has to be hung above a door and above and below a window, so the opening takes a piece out of the strip without removing the strip. On a 12 by 14 room a door and two windows are 11 percent of the area and nothing at all off the order. Only take out an opening wide enough to swallow whole strip widths, such as a patio door.
Multiply the wall run by the height: a 52 foot run at nine feet is 468 square feet. It is worth knowing for comparing prices, but it is the wrong unit to order by, because paper is hung in whole strips and a square foot figure cannot tell you how many strips a wall takes.
Measure the longest drop, from the upstairs landing down to the lower floor, and use that for every strip on that wall. You cannot cut a strip to a length you have not bought, so the tallest drop governs the whole wall and often gives that wall a different strips per roll figure from the rest of the house.
Two inches at each end of every strip for trimming, or four on an older house where the ceiling is not level. That is separate from the pattern repeat, which rounds the cut up again. Beyond that, order the whole job at once with matching batch numbers and keep the spare rather than returning it.