Estimating Wallpaper

Calculate the area of the project.
Measure the length and height of each wall you wish to cover in wallpaper. Subtract doorways and large windows from the total length. You can round the length measurement up to the nearest half foot or foot (or meter) to make it easier to calculate.
Multiply the length and width of each wall to get the area in square feet.
Add up the area of each wall to get your total area.
Increase the total area by 15 percent to account for waste.
You won't be able to estimate the amount of wallpaper needed until you know whether it has a straight match or drop pattern.
Look at the wallpaper packaging or on the back of the sample to find out the repeat length of a drop pattern.
Free Match means that the pattern is not intended to be matched longitudinally at adjacent lengths. In simple speak, it means no need to line up the paper and you won't get much waste on the roll!
Straight Match means you need to match the pattern on adjacent lengths without any longitudinal displacement. The length of the repeat is also expressed as a number e.g 64cm. This means that you must line up your pattern on the wall in straight lines. The length of the repeat can indicate how much waste you will have.
Offset Match means there is a longitudinal displacement in order to give the correct match on adjacent lengths. The amount of displacement is expressed as a number eg 64/32cm. 64cm is the pattern repeat, 32cm is the amount of displacement. In simple terms, the pattern will feature in diagonal lines.
These are the most common type of drops you will see on your wallpaper but there are two others:
Reverse each adjacent length would be reversed when hung.
Horizontal lengths are hung horizontally on the wall.
Verify the number of square feet each roll covers.
Rolls of wallpaper typically measure 33ft (10mtrs) long and 21" (535mm) wide and therefore cover an area of 37.62 sq ft or 5.35 sq mtrs.
Reduce the total usable square footage on a roll to account for a drop pattern, if applicable. If the wallpaper has a straight match, all of the paper will be used, however if there is a pattern repeat then the following usage applies based on a normal size room.
Typically
0" to 6" 25 sq. ft.
7" to 12" 22 sq. ft.
13" to 18" 20 sq. ft.
19" to 23" 18 sq. ft.
Calculate the number of single rolls needed. Divide your estimated total square footage by the number of usable square feet on a roll to get the number of single rolls needed for the project.