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Crochet hook sizes can be a bit confusing, especially if you are either new to crochet or live outside the U.S. and are trying to find the right size to follow an American pattern. I’ll explain the American crochet hook size system, and provide a conversion chart so that you can crochet with ease, no matter where you are!
American Crochet Hook Sizes
American crochet hooks go by two names: a letter and a number. For example, the crochet hook size that is most commonly used for worsted weight yarn is an ‘H’, which is sometimes called a ‘size 8’. From an international point of view, this number is incredibly confusing! Most countries identify crochet hooks by their size in millimeters (mm). A size H crochet hook is 5mm, which as you can notice, doesn’t clearly line up with the number ‘8’. However, this confusing notation isn’t a problem if you reference a conversion chart when you are ready to crochet.
Crochet Hook Conversion Chart
Click here to download my handy printable crochet hook size conversion chart. Not only does it convert between American letter/number sizes and mm – it also lists all the various yarn sizes and the many (many!) names each size can be called.
Use the chart to find the hook size called for by your pattern, and you will be able to identify the size (in mm) that you should use. This should allow you to find the hooks you need to crochet using American patterns, no matter where you are!
The chart also reveals a few other slightly confusing aspects of crochet hook sizes. 😛
You’ll notice that the difference in mm between two hook sizes is not a consistent difference. For example, the difference between a ‘B’ and a ‘C’ crochet hook is .5 mm. However, the difference between an ‘H’ and an ‘I’ crochet hook is 1.0 mm. This can make it difficult to remember all of the conversions, so be sure to check each hook size that you would like to convert. Usually, both the American size and the size in mm are written on the crochet hook package, so that’s a convenient place to check when you’re making a purchase.
Also – the very smallest crochet hooks are called steel crochet hooks and their sizing is different. They don’t include letters, and as the crochet hook gets bigger, the size number gets smaller. It’s weird, I know.
There are occasionally some differences in sizing according to various brands, but the chart includes the most common ones.
Want to learn more about crochet hooks? This post breaks down the anatomy of a hook and helps you choose which kind is right for you.
Finally – a reminder that all of this is just a guideline! The hook size called for in the pattern, on the yarn band, or in the chart is just a suggested starting place. Crochet a little swatch and adjust your hook size up or down as needed.
Now, you’re ready to start converting and crocheting!