Suture size is based on strength and diameter as decided by the United States Pharmacopeia (U.S.P.)  This system uses "0" as the baseline, average size suture.  As suture diameter decreases, "0's" are added or numbers followed by a "0" (for example, 000 and 3-0 are the same size).  As suture diameter increases above "0", numbers are assigned to the suture material.