The first thing you need are accurate measurements of the walls that are to be covered. Use a yardstick or steel tape measure. Measure in feet rounding off to the next highest half foot or foot. Draw a room diagram showing doors, windows and ceiling height. If there are built-in bookcases or a fireplace,for example, show those as well. Next, calculate the square footage of every wall that will be covered. Subtract areas that will not be covered. (Standard doors are about 3 X 7 feet or 21square feet; standard windows about 3 x 5 feet or 15 square feet.)
20′ + 20′ + 15′ + 15′ = 70′ room circumference
70′ x 8′ ceiling height = 560 sq. feet
2 standard windows = 30 sq. ft.
1 standard door = 21 sq. ft.
30′ + 21′ = 51 sq. ft.
560 – 51 = 509 sq. ft.
509 / 25 = 20.36 rolls
Divide this figure by 25, the number of square feet in a single metric roll of wallcovering. This gives you the approximate number of rolls needed. Note that the pattern repeat,rooms of unusual size or shape, greater than normal wastage during hanging, or other special circumstances can affect the rollage needs. Your local independent retailer can calculate your exact wallcovering needs based on the pattern you select and your room diagram.