How many rolls do I need

Rolls are 4 feet wide. This lays them in strips and rounds each strip up to a full roll. A leftover piece on one strip is not counted on the next. Color does not change the count. Grey is the 4' x 25' roll.

A room 12 feet by 16 feet takes 3 rolls of 4' x 16', one strip for each 4 feet of width.