The Size of a Knitting Needle or Crochet Hook
The size of the knitting needle or crochet hook that you use is crucial if you have any interest in replicating a pattern with precision or achieving a predictable fit. We alter our gauge (stitches per inch) by increasing or decreasing the size of our needles or hook to match the gauge listed in a pattern.
The only challenging thing about understanding hook and needle sizes is that there is no standard. Just as with more modern technologies, it’s hard for the amorphous world-wide group of individuals who decide what to call fiber crafting tools to agree upon a standard naming system (and stick with it). What any pattern calls a knitting needle or crochet hook of a certain size depends on several factors:
In what year was the pattern written? In what country was the pattern written? Which system was the pattern writer familiar with?
The issue is even more complicated by the fact that manufacturers of knitting needles may decide on their own standard if they wish. For instance, we carry needles from both Addi and Knitter’s Pride here at Over the Rainbow Yarn. Addi calls a needle measuring 3mm in diameter a US 2, and Knitter’s Pride calls a needle of the same size a US 2.5. Perhaps Knitter’s Pride or an earlier company set out with the noble goal of differentiating between the 2.75 and the 3.0mm needle, which were both called US 2 previously?
For crochet hooks, there are two separate sizing systems – one for the very small hooks which are typically used with thread and made of steel, and one for the larger hooks which are typically used with heavier yarn and made of aluminum, wood or plastic.
Some needle conversion charts include more or different standards from this one, such as Japanese sizes, French sizes, or old American sizes versus new American sizes. Old American sizes (from the mid-1900’s) are similar to the dual-system used for crochet hooks: a 2.5mm is a Size 1, and larger needle sizes increase to 2 and then 3, etc., but smaller sizes (for steel dpns) have larger numbers beginning at 12 and going up from there, much like wire gauge sizes. Don’t get old American sizes mixed up with UK sizes, though; for the small sizes, they are close but not the same.
The chart below covers the most common sizes you’re likely to run into in the English-speaking world, and in some cases includes common naming discrepancies. You can use it to convert sizes from one standard to another. Of course, the best way to be sure you’ve got the size you think you have is to know the actual measurement of your hook or needles in millimeters.