Crochet Hook Size Conversion Chart

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!

Variety of crochet hooks

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

Use the chart below to find the 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!

Crochet Hook Conversion Chart

American Letter
American Number
Millimeters (mm)










This chart also reveals another slightly confusing aspect of crochet hook sizes: you will 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 .5mm. However, the difference between an ‘H’ and an ‘I’ crochet hook is 1.0mm. 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 is a convenient place to check when you are making a purchase.

There are occasionally some differences in sizing according to various brands, but I’ve included the most common ones.

Now, you’re ready to start converting and crocheting!

20 replies on “Crochet Hook Size Conversion Chart

  • liz

    Hey there, I am making a beanie with an F hook. The pattern calls for J but it looked whack with a J; so I used the F. With the J hook, I can stop increasing size at sc9, 2sc in one. In your opinion, what does that convert to using my F hook? I was thinking adding 5 more rows, but would appreciate a second opinion.

    • Stacey

      Hi Liz-
      Changing gauge as it relates to a pattern is a complicated question… unfortunately, there’s no ‘one size fits all’ answer. You’ll have to experiment, do some calculations and see if it’s working for you!

  • Gale

    Hi, I am reading a pattern that calls for a Boye Steel Hook Size 1. I live in Canada and we do not have that brand of hook. Could you please tell me what size hook I would use?

    Thank you very much


  • My

    Hi! Your chart has been very helpful. I have a question though. I have a pattern that calls for a C hook (2.75mm) which I don’t have. I do have a steel size 1 hook which is 2.75mm and wanted to know if I could use the steel hook since it’s the same mm? Thank you.

    • Stacey

      That’s a really interesting question! Although my steel hooks are much smaller than a size C, my gut says that if you have one in the same mm size, then you can use it! I would pop by a store and look at a size C in person, though, just to make sure your size 1 is in the same ballpark.

  • Cynthia

    I was wondering if maybe you could help me, I am about to start working on a table cloth, and the pattern calls for a “Milward Stell Crochet Hook No. 5”. I cannot find a conversion for the Milward to just plain mm, I have seen 1.75 mm and then 0.75 mm. Do you know anything about it?

    • Stacey

      My guess is that the pattern is referring to a Steel Hook size #5. Those are not included on this chart, but they are sold in stores. I don’t think the brand name is very important.

  • sarahy j.

    hi tracy :) am making a shrug, the pattern ask for a n hook but i only have an L hook right now .do you think it would make a big difference on the work if i use a L hook instead of an N hook? thanks a bunch :)

    • Stacey

      Hi Sarahy- I always recommend that you use the hook size that gets you the gauge recommended in the pattern. Otherwise, you may end up with a shrug that doesn’t fit!

      • sally k

        I have a pattern asking for a 3mm hook. It’s for a baby sweater, hat and booties. Your chart doesn’t convert 3mm, any suggestions?

        • Stacey

          I would look online for a 3mm hook- different brands tend to offer different sizes.
          Otherwise, be sure you are doing a gauge swatch, you may find you need a different size, anyway!

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