Measure your wall first. Then add an extra 6 cm in width and 6 cm in height for cutting loss.
A patterned wallpaper (165 gm non-woven) roll consists of 2 strips, each 48.7 cm wide and 280 cm high. If your wall is 280 cm or lower, you get two strips from one roll. For technical reasons, the wallpaper can be 48.4 cm wide. So take extra margin anyway so you don't come up short.
Suppose you have a wall 342 cm wide by 262 cm high. Including the cutting loss, the required size is 352 x 272 cm. With this height, you get two strips from one roll. Now, divide the width of the wall by the width of the strip: 342: 48.7 = 7.22 = rounded up to eight strips. So in total, you need four rolls of wallpaper.
A Hotel Chique wallpaper or Natural Chique wallpaper roll is 53 cm wide and 10 meters long. If your wall is lower than 250 cm, you get exactly four strips from one roll. If your wall is between 251 and 333 cm high, you get three strips from one roll.
Suppose you have a wall 297 cm wide by 265 cm high. Including the cutting loss, the required size is 307 x 275 cm. With this height, you get three strips from one roll. Now, divide your wall width by the strip width: 307: 53 = 5.79. Let's round them up to 6 strips. So in total, you need two wallpaper rolls. The batch number on the roll shows from which print run the wallpaper comes. When you order multiple rolls, the rolls must have the same batch number to avoid small colour differences. Therefore, it is essential always to check whether the supplied rolls are from the same printing run before hanging the wallpaper.