With the exception of Oster and Andis brands, most standard clipper sets have eight guard sizes, the longest of which is 1 inch long. Clipper guards are numbered 1 through 8 and get longer in 1/8-inch increments.
The number 1 clipper guard measures 1/8 inch, the number 2 clipper guard measures 1/4 inch and so forth. While the number 8 guard is usually the longest guard that is sold in standard clipper sets, larger guards are available by special order. For example, Wahl offers numbers 10 and 12 clipper guards, which measure 1 1/4 inch and 1 1/2 inch, respectively.