Numerical labels like #1, #2 and #3 refer to the length of the paperclip. In terms of paper clip sizes in inches, No. 1 paper clips are 1 3/8” long, No. 2 paper clips are 1 1/8” long and No. 3 paper clips are 15/16” long. These paper clip sizes in cm translate to 3.49 cm, 2.85 cm, and 0.93 cm and paper clip sizes in mm translate to 35 mm, 28 mm, and 9.5 mm, respectively. We recommend paper clip sets that carry all or most sizes to suit all types of paper sizes and thickness.