Rubber bands are measured via three dimensions - Lenght (lay flat length), Width (cut width), and Thickness.
Pinch a rubber bands at each end as if to lay the band flat. The distance from end to end is the band length.
The width of the band measures how wide the band is, perpendicular to the length. The thickness measures the wall of the band. Thickness generally ranges from 1.1 mm - 2.5 mm.