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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. In this article, we will 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 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.

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)
B
1
2.25mm

C
2
2.75mm

D
3
3.25mm

E
4
3.5mm

F
5
3.75mm

G
6
4.0mm

H
8
5.0mm

I
9
5.5mm

J
10
6mm

K
10.5
6.5mm

This chart also reveals another slightly confusing aspect of the American sizing system: 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.

This isn’t all of the hook sizes there are! We have presented the hook sizes that are most commonly used for yarn. There is a different numbering system for ‘steel hooks’, or really tiny hooks used for crochet thread. There are also very large sizes of crochet hooks available. Again, the crochet hook package usually reveals the size in mm, so have a look if you are interested in these (very small and very large) sizes.

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

12 Responses to “Crochet Hook Size Conversion Chart”

  1. Adele Gilmore says:

    Thank you for this chart.

    By chance do you have one for tiny hooks?

    Adele

  2. liz says:

    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 says:

      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!

  3. […] Freshstiches.com has a pretty useful write up on hook sizes and conversions.  Take a look at Stacey’s site too (I love her designs!), while you are there. […]

  4. Gale says:

    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

    Gale

  5. […] Crochet Hook Size Conversion Chart | FreshStitches […]

  6. My says:

    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 says:

      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.

  7. Jane says:

    only one i found i understood, thank you

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