So in order to buy exactly as much as you need to complete the correct calculation of the required number of materials. As an example of counting, you can submit a calculation of the required number of wallpapers. So, in order to calculate how many wallpaper you need to measure the walls first, it means to measure their length and height, and then change the sum of all indicators, that is, the total length of all walls and the total height of all walls of the room, which will be glued to the wallpaper. As a result, the total area of all walls will be obtained.