How long is 10 feet?
Ten feet is equivalent to 120 inches or 3.333 yards or 03.048 m or 304.8cm or 3048mm.
Wallpaper usually is hung in a vertical manner: from the top of the wall to the bottom. If the wallpaper is 10 feet long, it means that it will cover a space that measures 10 feet or 120 inches. The specific measurement mentioned in the question means that piece of wallpaper will cover an area 10 feet tall and 9 feet wide.