How to Determine the Quantity of Wallpaper Needed

Measure the ceiling height of the room you plan to wallpaper. For our example, we'll use a ceiling that is 9 feet in height.

Determine the width of each wall by measuring along the floor from edge to edge and round up to the nearest foot. For our example, we'll use a room that is 11 feet wide by 13 feet long.

Calculate the square footage of the 11-foot wall: 11 foot wide times 9 foot high equals 99 square feet per wall.

Multiply the results by two to include the opposite wall: 99 times 2 equals 198 square feet.

Repeat the process for the length of the room: 13 feet long times 9 feet high equals 117; 117 times 2 equals 234 square feet.

Add the square feet of the walls together: 198 plus 234 equals 432 square feet of total wall space.

Subtract any large areas such as a picture window by figuring the square footage of the window and subtracting it from the total wall space. For example, a window that is 6 feet by 5 feet would be multiplied 6 times 5, which equals 30. Subtract the window area: 432 minus 30 equals 402 square feet of wallpaper needed.

Divide the amount of square feet per roll of wallpaper into your total square feet of wall area, and then round up to determine how many rolls of wallpaper you need to purchase. For example, a typical roll of wallpaper is 35 square feet. Divide 402 by 35, which equals 11.49; round up to the next whole number: 12. That means you'd need 12 rolls of wallpaper to complete the job.