This wallpaper roll estimator provides the minimum amount of rolls needed to cover the wall surfaces. It accounts for the roll dimensions and pattern repeats in standard rooms (either accent walls or rectangular rooms). This estimator does not account for doors and windows, attic stock, or manufacturer defects. In practice, my installation prices are based on the minimum amount of wallpaper needed to complete the installation but I try to order at least one extra roll to mitigate the risk associated with ordering extra material that may not be in the same production lot (and may not match color). Many retailers offer a restocking fee for returned rolls, typically 25% of the retail price. It's typically a good call to order the extra roll; it's among the cheapest insurance policies against shading issues.
This application is a practical implementation of the estimation techniques discussed in the 'Measuring Wallpaper' article available on the blog. For a deeper understanding of these techniques and more detailed guidance on accurately measuring your space, please refer to Measuring Wallpaper.