Knitting needles are long thin shafts that taper at one or both ends. The sizes of knitting needles are based on various gauges depending on the purpose. The gauge specifies the diameter of the shaft, with smaller sizes being used for finer knitting projects. Gauge systems vary from one country to another. Wolfram|Alpha provides the ability to do knitting needle size conversions between the various systems.
Knitting needle sizes are specified according to a gauge, which can be compared to other gauges used by wires, drills and meshes.