Firstly measure your wall lets use an example here of 4.2 wide by 2.5 high
On each product page is the description of that wallpaper. To place a wallpaper order you need check:
Roll size: It might say for example 53cm x 10m
Each roll is therefore 53cm wide. From that roll you will get 4 drops of wallpaper on your wall – 10 divided by 2.5 = 4
Which is correct if there is no pattern repeat.
Pattern repeat: This is where during the installation each drop will have to be aligned to match the pattern on the previous drop.
This needs to be calculated too. So if the pattern repeat on the 53 x 10 roll is 53cm you need to add that on to the wall height – 2.5 + 0.53 = 3 m. This tells us that you will now only get 3 drops from the roll.
Finally your wall is 4.2 wide divide that by the rolls width of 53cm = 7.92 and is rounded up to you needing 8 drops altogether. 8 divided by 3 = 2.66 and is rounded up to you needing to order 3 rolls.