Enter the room and roll sizes, including any pattern repeat, and get the number of wallpaper rolls to buy.
Wallpapering is worked in drops (full-height strips), not just area. The calculator divides the room perimeter by the roll width to get the number of drops, then works out how many usable drops fit in one roll: each drop needs the wall height plus trimming allowance, rounded up to the next full pattern repeat so the design matches across strips. Doors and windows reduce the material needed by their share of the wall area. All rolls for one room should share a batch or lot number so the print shade matches.
Why does a pattern repeat use more paper? Each drop must start at the same point in the design, so offcuts up to a full repeat long are discarded at every strip. A large repeat can add a whole extra roll to a room.
How many drops come from one roll? Divide the roll length by the drop length (wall height plus trimming, rounded up to the pattern repeat). A 33 ft roll on an 8 ft wall usually gives three full drops, sometimes four with no repeat.