Convert US knitting needle sizes to millimetres.
Knitting needles are sold in US sizes, metric sizes in millimeters, and old UK sizes that run the opposite way. The metric size is the true diameter, and it is the best way to compare needles from different countries. This calculator converts a US needle size to millimeters.
For example, a US size 6 is 4.0 millimeters, a size 7 is 4.5, a size 8 is 5.0, a size 9 is 5.5, and a size 10 is 6.0. Some sizes, such as US 10.5 at 6.5 millimeters, fall between the whole numbers.
The yarn label suggests a needle size, but the right size for you depends on how tightly you knit. Knit a gauge swatch and measure the stitches over four inches, and if you have too many, go up a needle size, and if you have too few, go down.
Needle type matters as well. Circular needles suit large projects and knitting in the round, double pointed needles suit small circles such as socks and sleeves, and straight needles suit flat pieces. Bamboo needles grip the yarn more, and metal needles let it slide fast.