Once you’ve found the perfect wallpaper, the next step is to figure out how much wall you have to cover. I’ll teach you how to determine the total square footage of the area you want to wallpaper. Give this number to your installer, or use it yourself to figure out how much wallpaper to buy.
Pull out your tape measure and follow these instructions.
(Note: This process will work for most walls. But see below for special instructions if your wall has large windows, doors or built-ins, etc.)
First, measure the height of the wall. Omit any crown molding or baseboards, and round up to the nearest inch.
Next, measure the width of the wall. If there are any basic windows or doors, ignore them. Again round up to the nearest inch.
Multiply the height of the wall by the width of the wall and divide by 144. This will give you the total square footage of the wall. Round this number up to the nearest square foot. (A note for the curious: There are 144 square inches in one square foot. We divide the total square inches by 144 to convert it into total square footage.)
Height = 8” 2.5” → 99”
Width = 10” 4” → 124”
Total square footage = 99” x 124” = 12,276/144 = 85.25 → 86 square feet
Repeat this process for every wall you are covering and add up the square footage to get the grand total.
Measuring Walls With Large Windows, Doors, or Built-Ins
As you wallpaper around a room and reach a window, you will still need a full strip of paper to keep the pattern going. That’s why we ignore single doors or windows in our measurement—you still have to order the same amount of wallpaper to get that usable strip; you aren’t going to find any company that will cut that part out for you and charge you less.
However, the calculation changes if you have a large swath of wall that won’t be covered by wallpaper—say, a huge bank of windows, a section of built-in shelves, or a large sliding door. We call this “negative space.”
You could factor the negative space of your total square footage to save money. My general rule of thumb is if the negative space takes up at least half of the wall, factor it out.
Measure the height and width of the negative space in inches. Multiply those two numbers, then divide the total by 144 to get the square footage of the negative space. Using our previous example, let’s add in a sliding door to that wall that is 66” wide and 90” tall.
Wall = 86 square feet
Door = 66” x 90” = 5,940/144 = 41.25 square feet → 41 square feet (I round down for negative spaces to make sure I’m not subtracting too much from the total)
86 – 41 = 45 square feet total
Hopefully this guide, while simple, will help you feel more confident in doing your own measurements. There are other unusual shapes and circumstances that I haven’t covered here, such as stairways and slanted ceiling lines. If you find yourself stumbling upon one and need some help figuring it out, feel free to leave me a comment.