Read a standard needle size chart by comparing a needle to the related conversion. For example, a U.S. size 0 needle is a metric size 2.0 mm or a UK/Canadian size 14. Yarn Forward and Sew It Love It both offer needle size charts on their respective websites.
Yarn Forward’s needle size chart features the standard conversions of needles from one size to another. To read the chart, find the needle you wish to convert based on its size. For instance, if your needle is a 4.0-mm needle, find 4.0 in the Metric Sizes column, move down the column to 4.0, and discover the conversions to U.S. and UK/Canadian sizes. The 4.0-mm needle converts to a U.S. size 6 or a UK/Canadian size 8 needle.
The chart on Sew It Love It is a bit more comprehensive and offers examples of fabric weights and examples of fabrics that require the particular needle size. To use Sew It Love It’s chart, find the size of the needle in either the American Sizes or European Sizes column, and view information about uses for the needle in the Fabric Weight and Fabric Examples columns. For example, a U.S. size 10 needle works well with very thin fabric, such as chiffon, organza, silk and fine tricot, according to the chart.