Needle Size
The thickness of the knitting needles, measured in millimeters (mm), US sizes, or UK sizes.
Explanation
Needle size indicates how thick the knitting needles are. Most of the world uses metric sizes (mm), while the US uses a number system (US 0-15) and the UK has its own system. Needle size affects your gauge: thicker needles result in looser stitches and a larger garment, while thinner needles result in tighter stitches and a smaller garment. If your gauge doesn't match the pattern, you must change your needle size.