Knitting needles sizes are calculated by their diameter, whether it's a pair of single-pointed needles or circulars or even a set of double points. There are two measurements on most knitting needles, one in millimeters and one that is usually in the US followed by a number. Understanding knitting needle sizes are very important for the success of knitting projects. To know more, follow our blog. https://www.lanternmoon.com/blogs/blog-post/understanding-knitting-needle-sizes