How to calculate the amount of wallpaper you need

Tim Hogan, owner and president of WallpaperProPainting.com in Kansas, says plenty of his customers order the correct amount of wallpaper after doing their own measuring. However, he also says 30 to 40 percent of them get it wrong.

Measuring for wallpaper is a completely DIY-friendly task. Hogan has a method he says delivers more accurate results than measuring square footage. And that’s what you want, right?

How Much Wallpaper Do I Need?

Most wallpaper measuring guides advise calculating the square footage of your wall. Hogan says this can leave you with too little wallpaper. Instead, he recommends determining how many strips you need to place around the room, then calculating the number of usable, floor-to-ceiling strips on each wallpaper roll.

The goal, Hogan says, is to make each vertical strip of wallpaper one piece, without a seam in the middle.

Calculating square footage can leave you short because you’ll trim off some paper to make the pattern line up, but you can’t combine two leftover pieces to make a new floor-to-ceiling strip without a seam. Some of the square footage on your roll will end up in the garbage.

How to Measure for Wallpaper: Linear Feet Method

Measuring for linear feet is a simple way to calculate the number of wallpaper strips needed to cover the space, Hogan says. Then measure the height of your walls to determine how many usable strips you have on each roll.

The tools you’ll need:

• Tape measure.
• Your phone’s calculator.
• Your phone or a pencil and notepad for recording measurements.
• The wallpaper roll’s length, width and pattern repeat, i.e. the distance between a repeating pattern that must line up across the wall.

Then follow these steps:

• Measure the width of each wall you’re wallpapering with the tape measure. Record these.
• Add the widths together and record the total.
• Measure the height of your walls and record.

Note: Don’t exclude things like windows and doors. You’ll cut them out of the wallpaper as you hang it, unless they happen to line up exactly with the edge of a strip of paper. If your wall has different heights — say, if you have a sunken living room or a vaulted ceiling — measure to the highest point.

How to calculate the number of wallpaper rolls to order

1. Divide the total width of your walls by the wallpaper’s width. This is the number of floor-to-ceiling wallpaper strips you need to cover your walls. So 44 feet divided by 2.5 = 17.6.

2. Add the height of your walls to the pattern repeat to determine the adjusted height. Eight-foot ceilings + a 36-inch pattern repeat = 11 feet. This adjusted height accounts for potential waste as you line up the pattern on the walls and trim off any excess.

3. Divide the length of the wallpaper roll by the adjusted height in Step 2. Round down if you have a remainder. This is the number of usable strips on each roll. Thirty-three feet (the common length of a double roll) divided by 11 feet = 3.

4. Divide the number of strips you need (see Step 1) by the number of usable strips on each roll (Step 3). Round this number up to determine the number of rolls you need to buy. So 17.6 divided by 3 = 5.87.

5. Add one roll to account for mistakes in measurements or installation. In our example, we’d order seven rolls.

Does Wallpaper Need to Be From the Same Batch?

It’s important to order all the wallpaper you need at the same time because there are often slight variations between batches, says James Greenwood, brand manager for wallpaper maker Graham & Brown. If you place a second order from a different batch, you could end up with slight color shifts.

Most sellers will take back unopened rolls if you order too much. Check your seller’s policy before ordering.

Greenwood and Hogan recommend ordering one extra roll. Greenwood also suggests keeping leftover wallpaper on hand after your project is done. “If some food or some tea or coffee gets spilled on the wall, I know I have a strip from the correct batch,” he said. You can also repair damaged wallpaper when you have some left over.

Common Wallpaper Measuring Mistakes

Most measuring mistakes Hogan sees involve pattern repeats or confusion over single vs. double rolls.

A pattern repeat is the vertical height of a pattern. Each piece of wallpaper hangs flush horizontally, with some excess trimmed off the top or bottom. “The bigger the pattern, the more waste because you’ll cut off more paper to get the pattern to line up,” Greenwood says.

Wallpaper used to be sold in single rolls of 12 or 13 feet, Hogan says. Now it’s typically sold in double rolls of about 26 feet. Yet Hogan says some companies advertise prices for single rolls while only selling them as doubles, confusing consumers. That’s why he recommends paying careful attention to wallpaper specifications as you calculate what you need.

It’s also important to take your own measurements. While many wallpaper sellers offer basic measurement tools on their web sites and apps that estimate how much you need based on square footage, measuring yourself gives you more precision.