The Ultimate Crochet Hook Conversion Chart (US, UK, Japan!)

Why are there so many crochet hook size measuring systems? All these different measurement systems can make figuring out what size of crochet hook you need a painful process. To help you out, check out the master conversion chart below.

3/0132.25mm– –
5/0113.00mm– –
– –103.25mmD/3
– –55.50mmI/9
– –36.50mmK/10.5
727.00mm– –

But really, why are there so many different systems for measuring crochet hooks, and why is converting between them so complicated? There’s got to be some reason behind this complex mess! Let’s break it down.

Why Do Different Countries Have Different Names for the Same Hook Sizes?

For most of the history of crochet, there was no standard in the crochet hook manufacturing industry. Naturally, this led to different countries adopting different naming conventions for the sizes of their products.

This has also led to some sizes not actually being sold in some countries, such as the 6.50mm in Japan or the 7.00mm in the US. The most standardized system of measuring crochet hooks is still the metric system, to and from which it is fairly simple to convert any size.

In the United States, we use letters to represent the different sizes, while in the UK they use descending numbers from fifteen to triple zero. The Japanese convention goes from using a number over zero for smaller sizes and a whole number counting up from seven to measure larger needles.

These naming conventions are fairly arbitrary, and honestly, the metric system is probably more useful than all of them combined for actually figuring out how big of a needle you need. This is because all of the other measuring systems use millimeters as their base.

Where to Buy Japanese/UK Crochet Hooks

It’s tough to find foreign crochet hooks in the United States at local stores. Even if you can, you’ll need to bring your conversion chart with you so you can interpret the American sizing on the package into whatever you’re looking for for your pattern.

More importantly, you might be looking for one of the sizes that aren’t included in the American system. If this is the case, you’ll want to look online.

If you’re looking for Japanese products, Amazon and Aliexpress are both good options. Aliexpress has a better variety of Asian products, while Amazon has the advantage of faster shipping and perhaps a more familiar UI.

Rakuten also has a great selection of Japanese crochet hooks, but shopping on Rakuten can be an overwhelming experience for many Americans. You also need to use a proxy shopping service like if you want to have your stuff shipped to the United States.

Of course, none of this is necessary if your preferred Japanese crochet hook brand is something like Hamanaka, which is fairly popular in the United States, making it a lot easier to buy here compared to some other Japanese brands.

As for UK or European crochet hooks, the best bet is Amazon. There aren’t as many options for shopping specifically European—this is mostly because European products are more likely to be imported anyway, which does make them a bit more accessible.

What Do They Use in Countries Other Than the US, UK, or Japan?

In most other parts of the world, people measure their crochet hooks with the metric system. This is great if you’re working with patterns from those parts of the world, as the metric system is the easiest of all of the different ranges to convert to or from.

Other Regional Crochet Terms

Like with many other terms in the English language, there are a lot of different regional dialect terms when it comes to crocheting. This can lead to some confusion when working on a pattern from the UK as an American, or vice versa.

Sometimes it seems like these terms are just Americans trying to bother English people by saying weird things like Half Double Crochet, which seems like it would just be a single crochet, but actually equates to the English term Half-treble.

Here’s a handy chart you can use to go between the two when you’re looking at a pattern.

Single CrochetDouble Crochet
Half-Double CrochetHalf-Treble
Double CrochetTreble
TrebleDouble Treble
Double TrebleTriple Treble
Yarn OverYarn over hook

Japanese Crochet Terms

Looking at a Japanese crochet pattern can seem pretty overwhelming, considering just how different they are compared to English patterns. To help with this, here are a couple of symbols that might be useful for you to know.

Open-Ended Oval:

An open-ended oval calls for a chain stitch, while a closed oval indicates a slip stitch.


The X and + symbols in Japanese patterns both mean a single crochet stitch.


The T and slanted T symbols represent a half-Double crochet stitch and a double crochet stitch. Sometimes these symbols are arranged in a V shape, which indicates an increase, while the opposite of that represents a decrease.


Here’s a list of useful numbers:


A lot of times there will be Japanese writing in the patterns. You don’t really need to be able to read anything but the numbers, which will tell you important quantities, like the amount of wool to use and the number of stitches you use.

Japanese numbers stack a little differently than English numbers do. Rather than simply sticking two numbers together to form numbers higher than ten (23, 47, 135), in Japanese, ten is written after the ten’s space, one-hundred after the hundreds space, thousand after the thousands, and so on. This means that the number 173 would be written out as:

一百 七十三

It also might just be written out in western numbers, as most Japanese people can read western numbers just as well as traditional Japanese numbers.