Tarps can also be classified by size-a common determining factor for consumers in acquiring tarps-and measured in width by length. Actual tarp sizes are generally about three to five percent smaller than the advertised size. (Thus, a tarp advertised as 20 ft. × 20 ft. will actually measure about 19 ft. × 19 ft. Some other factors that may influence a purchase decision include color (often they come in blue, green, black, or silver), grommet type (aluminum, stainless steel, etc.), and grommet-to-grommet distance (these often run between 18 inches and 5 feet).