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Crochet Hooks Chart with US/UK/mm Conversion + The Difference Between Thread Crochet Hooks and Yarn Crochet Hooks

We often get questions about how to read a crochet hooks chart. This is a chart that shows you the different sizes of crochet hooks. Moreover, it shows those sizes in different versions: UK and US. Additionally, you’ll see letters (hook size B or G, for example.) Moreover, you’ll see sizes in millimeters. It can all get really confusing. Then when you start looking at thread crochet hooks, which are totally different size-wise from yarn crochet hooks, this really get confusing. Well, we’re here with our crochet hooks chart to demystify all of this for you.

NOTE: You’ll see image versions of our regular and thread crochet hook charts below. However, you can also download a printable PDF version right here:

Choosing The Right Crochet Hook Size

As you know, you’ll use different sizes of crochet hooks for different yarn weights. Of course, you can use pretty much any size hook with any size yarn to achieve different effects. However, if you’re working to get specific gauge or to use the hooks in the traditional way, then you’ll use specific sizes of crochet hooks with specific yarns.

See our yarn weight chart here. It explains the different yarn weights. Moreover, it has suggestions for the types of yarn used for each crochet hook size.

Thread Crochet Hooks vs. Yarn Crochet Hooks Sizing

As you’ll see from our crochet hooks charts here, there is an important distinction to be made when it comes to thread crochet hooks vs. typical yarn crochet hooks. Now, to be clear, the hooks themselves are basically the same other than size. Thread crochet hooks are smaller (obviously, because thread is thinner.) They’re usually made of steel. In contrast, classic yarn crochet hooks are bigger and may be made of aluminum, bamboo, plastic, etc.

Crochet Hook Sizes Grow Bigger for Thicker Yarn

However, there’s a very important difference when it comes to sizing and crochet hooks charts. Typical crochet hooks used for yarn will grow in size as the yarn gets thicker. So, for example, if you look at the aforementioned yarn weight chart, you’ll see that you’ll usually use a size range of B1 – E4 (2.25 – 3.5 mm) when working with a #1 weight super fine yarn. (We’ll cover exactly what those numbers mean momentarily.) In contrast, you’ll usually use a size range of I9 – K 10.5 (5.5 – 6.5 mm) when working with a #4 worsted weight yarn.

This should feel fairly intuitive. If you’re working with a thinner (smaller) yarn, then you’ll use a crochet hook size that’s smaller. Even if you don’t understand the labeling just yet, you can tell that B-E, 1-4, and 2.25 – 3.5 are all smaller than the !-K, 9-10.5, and 5.5 – 6.5 mm ranges for the thicker worsted weight yarn. Thinner yarn, smaller letters and numbers; thicker yarn, larger letters and numbers. So, if you’re working with a yarn and you feel like the hook is too small for the thickness, you’ll go up in size.

Thread Crochet Hook Sizes Are Counterintuitive

Now, this is where it gets confusing. Here are three key things to know to get you started:

Crochet thread is assigned a number related to its thickness.

The thickest threads are #3, #5, #8, #10. After that, it increases in digits of ten as it gets thicker. So #20 thread is thinner than #10. Then #30 thread is thinner than #20. And so on up to the thinest of the threads: #100. This is counterintuitive, right? You would think: thinner thread, smaller number. After all, smaller yarn, smaller weight number right? DK weight yarn is a #3 and that’s thinner than Bulky yarn which is a #5. Not the case with thread. With thread, a bigger number means a thinner yarn.

Smaller crochet thread hook numbers work with thicker threads.

As you can see from the thread crochet hooks charts we’ve attached here, if you’re working with a size #3 thread then you’ll use a US size O, 1 or 2 thread crochet hook. On the other hand, working with a size #10 thread, you might use a US size 6, 7, or 8 thread crochet hook.

You use a bigger number hook with a bigger number thread. That at least makes sense – except of course for the weird fact that the bigger number thread is actually thinner. So the bigger number hook is actually smaller. But, so far, so good. At least these things match, right? So as soon as you get used to the idea that bigger means smaller in thread crochet (but not yarn crochet hooks), you can catch on.

Except … when you look at the millimeters

As you can see from our crochet hooks charts, there are all sorts of letters and numbers assigned to hook sizes. Among those are millimeters. Remember over on the yarn weight charts, we talked about how you might use a 2.25 mm crochet hook for lightweight yarn while using a 5.5 – 6.5 mm crochet hook for worsted weight yarn. Makes sense.

And, thread crochet hooks follow the same math. You’ll use a smaller millimeter range for thinner thread. Of course, then, the millimeters are higher for thicker thread. But this is where you can get confused again, right? Because when you look at our thread crochet hooks chart, you see that the hook sizes and thread sizes are increasing as the thread gets thinner … but the millimeters are decreasing! It’s obvious that you need smaller millimeter hooks to grab thinner thread. It’s just weird that thinner thread is a higher number and thus corresponds to a higher US number hook.

But now that you know those three key things, you can better understand thread crochet hooks.

Yarn Crochet Hooks Chart

Here’s a glance at our crochet hooks chart for yarn. Remember you can also download the printable PDF file:

Crochet Hooks Chart Part 1
Crochet Hooks Chart Part 2

Okay, So What Do All The Numbers and Letters Mean on Crochet Hooks?

If you’ve studied crochet for very long the you know that there’s a slightly different language between US and UK crochet patterns. It’s very similar, but different enough that you need to know the conversion between them to follow a pattern written in the language you’re less used to. Well, it’s the same way with the hooks we use. That’s why crochet hooks charts show US and UK sizes. They also show the millimeters.

US Crochet Hooks Sizing

US crochet hooks use a letter + number system. So a small US crochet hook is a B-1 or a C-2. A medium US crochet hook is a G-6 or an H-8. A large crochet hook might be an N-15 or P-16. (There are larger ones, such as Q or S, which aren’t usually assigned a number.)

UK Crochet Hooks Sizing

UK crochet hook sizes don’t use letters. They only use numbers. However, to make things confusing, their numbers work backwards on crochet hooks for yarn. The highest numbers are for the thinnest yarns, whereas the smaller numbers are for thicker yarns. Kind of like how we do with the thread crochet hooks. So, a small UK crochet hook might be a #13 or #12. In contrast, a medium UK crochet hook might be #7 or #6. Continuing on, a large UK crochet hook might be size 2. Note that there are no UK sizes comparable to the largest US crochet hooks sized US L-11 and up.

Crochet Hooks Sizing in Millimeters

The millimeters make a lot more sense because they’re very straightforward. As explained before with thread crochet, the thinner the thread, the smaller the number of millimeters. This should be obvious – you want a smaller circumference hook for smaller thread to make tighter pieces. It’s the same with millimeter numbering in crochet hooks for yarn.

So, working with a thin yarn, you might use a 2.5 or 2.75 mm hook. Working with a medium worsted weight yarn, you might use a 4.25 or 4.5 mm crochet hook. Then working with a bulky yarn, you might use an 8 mm crochet hook.

Reading a Crochet Hooks Chart

Most crochet hooks come with the US or UK sizing as well as the millimeters. So honestly, if you can learn which millimeter size goes with which thread and yarn size, you’re usually all set. However, most of us get comfortable working with either the letters or numbers from the US and UK crochet hooks. Moreover, what if you come across an amazing set of crochet hooks that are numbered different from what you’re used to? For example, you love a set of UK crochet hooks but are used to US numbering. That’s where it comes in a lot of handy to be able to read a crochet hooks chart.

We’ve created out detailed crochet hooks charts to allow you to easily see the difference between US / UK / mm along with suggestions for the thread # or yarn weight that you’ll use with them. So, let’s practice. You have a worsted weight yarn – what crochet hook size will you use? (Note that there are varied answers because there’s a range.) One good answer would be that you’d use a US Size H-8 crochet hook, which is a the same as a UK size 6 crochet hook, which is also the same as a metric size 4.75 or 5 mm crochet hook.

Thread Crochet Hooks Chart

Here’s a look at our thread crochet hooks chart. Remember you can also download the printable PDF file.

Thread Crochet Hooks Chart Part 1
Thread Crochet Hooks Chart Part 4

Reading Yarn Labels for Hook Size

When you read a yarn label, it often tells you the recommended crochet hook and knitting needle sizes. For example, a Chic Sheep yarn label recommends that this worsted weight #4 yarn use a 5 mm or size H-8 crochet hook. That corresponds with the example that we gave above. Moreover, referring to either that example or our crochet hooks charts, you can see that you could also substitute a UK size 6 crochet hook.

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Sources that helped in making our charts: The Spruce Crafts, Annie’s, All Free Crochet, and Craft Yarn Council.

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Marly Bird

The One and Only, Marly

Marly is a knitwear and crochet designer (and yarn addict) that is here to help you learn how to knit and crochet in a way that's fun and approachable.

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