Needle sizes, yarn weights and conversion charts: the numbers you need to match yarn, needles and pattern.
DK ("double knitting") is a light, category 3 yarn, slightly thinner than worsted. Its gauge, needle size, what to make with it, and how it compares.

Worsted weight is the most popular yarn weight, a medium, category 4 yarn. Its gauge, needle size, what to make with it, and how it compares to aran and DK.

A clear yarn weight chart from lace to jumbo, with gauge, recommended needle sizes and what each weight is best for. Plus how to find the weight of any yarn.
Fingering weight is a fine, category 1 yarn, the standard for socks and shawls. Its gauge, needle size, what to make with it, and its other names.
Convert knitting needle sizes between US, UK (old Imperial) and metric mm in one clear chart. Plus which needle size to use for each yarn weight.