1. Calculate the wall area by multiplying its height by the width.
2. Similarly, calculate the area of the wall you will not be papering; ie windows and doors.
3. Subtract the unpapered area from the total wall area to get the wallpapering area.
4. Divide the wallpapering area by the square footage of the wallpaper you would like to purchase. This will give you the total number of rolls needed for your project. Remember to consider extra paper for the pattern repeat and extra trimmings.