Needles that are used for venipuncture are available in a variety of lengths and diameters. The diameter of the needle is referred to as the needle gauge; the larger the diameter of the needle, the smaller the gauge number. The image on this page illustrates the relative gauges of needles that are available for venipuncture.
Needles that are routinely used for venipuncture are available in 3/4 inch, 1 inch, and 1 1/2 inch lengths. The phlebotomist determines the gauge and length of the needle to use for a venipuncture after assessing the vein.