One of the very first things you’ll need to figure out for a crochet project is the right hook size to use. This can be confusing because of the wide variety of sizes of different crochet hooks.
Crochet hooks can be labeled with letters, numbers, and millimeter (mm) sizing. This handy guide will help you compare crochet hook sizes and pick the right hook.
So if you need to know how many millimeters a particular U.S. size hook is, it will have you covered. And vice versa. Plus, you can download handy crochet hook size charts too!
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In this guide, you’ll find the following information:
- U.S. Hook Sizes
- Metric Hook Sizes
- Conversion Between the Systems
- Standard Crochet Hooks Chart
- Steel Crochet Hooks Chart
- How to Work a Gauge Swatch
- Crochet Hooks for Various Yarn Weights
- Frequently Asked Questions
U.S. Hook Sizes
In the United States, hook manufacturers generally use a letter size and/or number sizing. This system evolved because different crochet hook brands used different systems for labeling their hooks.
A currently-produced U.S. crochet hook will also show the millimeter (mm) sizing.
One of the most common sized hooks in the U.S. is the H hook. A U.S. hook size might include a label like “H/8 – 5mm” for this hook. If a U.S. hook has both a letter and number, they will often be listed together.
If you’ve grown up crochet in the U.S., this will all make sense. You’ll be able to read U.S. crochet patterns and figure out the hook by the letter and number.
Because of the variations, relying on the millimeter sizing will give you the most accurate measurement. For patterns from countries using the metric system, you can also use the mm sizing on a U.S. hook to find the right hook size for your pattern.
Metric Hook Sizes
Other parts of the world rely on the metric system. You will find hooks labeled with their millimeter size.
The millimeter size refers to the diameter of the shaft of the hook. This system is more precise than the letter and number sizing in the United States.
Because it gives you the size of the shaft, there should be no variation between hooks that use metric units.
You can also use a hook gauge tool to figure out the size of your hook. Below is a picture of a hook gauge tool that works for both knitting needles and crochet hooks.
To use the gauge tool, insert the knitting needle or the crochet hook into the different holes on the tool until you find where it fits. This gives you the size of the knitting needle or crochet hook.
If you don’t have access to a hook gauge tool or want to verify hook gauge, a conversion chart can be helpful if you’re in a metric system country and want to try a U.S. crochet pattern.
Conversion Between the Systems
A crocheter should be able to try a pattern no matter whether it originates in the United States or a metric system country. Getting the right crochet hook size matters so that you can produce projects that fit or that come out to the measures you want. So being able to convert from a metric to a U.S. sized hook and vice-versa is one of the crochet essentials.
A good crochet pattern will list a recommended hook size in both U.S. terms and millimeters. This is a great place to start to determine which hook to use for your crochet projects.
You can use this conversion charts to help you go from U.S. to metric terms and back gain. Then it’s a good idea to check your gauge to make sure you have the right hook for your project.
Standard Crochet Hooks Chart
This first chart is for standard or regular crochet hooks. These hooks can be made from different materials like aluminum, wooden, or plastic hooks. These are the hooks that you would use for most patterns like shawls, hats, and home decor projects.
The chart goes from the smaller sizes that you would use for a lighter yarn weight. And it goes to larger hook sizes that you would use for thicker yarns. The metric sizes are on the left. The U.S. sizes in letter and number are in middle columns. The chart also lists the older UK size in the last column
Standard Crochet Hook Size Conversion Chart
| Millimeter Range | U.S. Size Letter | U.S. Size Number | Old UK Size |
| 2.25 mm | B | 1 | 13 |
| 2.50 mm | 12 | ||
| 2.75 mm | C | 2 | |
| 3.00 mm | 11 | ||
| 3.125 mm | D | ||
| 3.25 mm | D | 3 | 10 |
| 3.50 mm | E | 4 | 9 |
| 3.75 mm | F | 5 | |
| 4 mm | G | 6 | 8 |
| 4.25 mm | G | ||
| 4.50 mm | 7 | 7 | |
| 5 mm | H | 8 | 6 |
| 5.25 mm | I | ||
| 5.50 mm | I | 9 | 5 |
| 5.75 mm | J | ||
| 6 mm | J | 10 | 4 |
| 6.50 mm | K | 10 1/2 | 3 |
| 7 mm | 2 | ||
| 8 mm | L | 11 | 0 |
| 9 mm | M/N | 13 | |
| 10 mm | N/P | 15 | |
| 11.50 mm | P | 16 | |
| 12 mm | |||
| 15 mm | P/Q | ||
| 15.75 mm | Q | ||
| 16 mm | Q | ||
| 19 mm | S | ||
| 25 mm | T/U/X | ||
| 30 mm | T/X |
If you look at the chart, making conversions will be easy. You can look at the chart to make conversions and find the right size hook.
Remember that in the U.S. system, a hook will often include both its letter and number together. For example, hooks will be called B-1, C-2, D-3, E-4, F-5, G-6, H-8, and so on.
For example, you may be asking:
- How many mm is a size H crochet hook? It’s 5 mm.
- What is a 5.5 mm hook in U.S. terms? It’s an I-9 hook.
Some questions won’t have ready answers. This is because the two systems do not directly translate to each other. This can raise lots of interesting questions about what size hook to use for a particular pattern.
The best way to determine what hook to use in these situations is to work a gauge swatch. The frequently asked questions section below also answers some of these more challenging questions.
Steel Crochet Hooks Chart
This second chart is for steel thread hook sizes that you would use for crochet thread or lace crochet projects. This chart also goes from the smallest steel hooks to the larger hooks. These are hooks you might use to crochet jewelry or for other thread crochet projects.
Interestingly, in the U.S. system a larger number for steel crochet hooks means a smaller size. This becomes clear when you look at the conversion to a mm hook.
Steel Crochet Hook Sizes Conversion Chart
| Millimeter Range | U.S. Size Range | UK Steel Size |
| 0.60 mm | ||
| 0.75 mm | 14 | |
| 0.85 mm | 13 | 7 |
| 0.90 mm | ||
| 0.95 mm | ||
| 1 mm | 12 | 6.5 |
| 1.05 mm | ||
| 1.10 mm | 11 | 6 |
| 1.15 mm | ||
| 1.25 mm | ||
| 1.30 mm | 10 | 5.5 |
| 1.40 mm | 9 | 5 |
| 1.50 mm | 8 | 4.5 |
| 1.60 mm | ||
| 1.65 mm | 7 | 4 |
| 1.70 mm | ||
| 1.75 mm | ||
| 1.80 mm | 6 | 3.5 |
| 1.90 mm | 5 | 3 |
| 2 mm | 4 | 2.5 |
| 2.10 mm | 3 | |
| 2.20 mm | ||
| 2.25 mm | 2 | 1.5 |
| 2.35 mm | ||
| 2.55 mm | ||
| 2.70 mm | ||
| 2.75 mm | 1 | 1 |
| 3.25 mm | 0 | 0 |
| 3.50 mm | 00 |
How to Work a Gauge Swatch
Working a gauge swatch is relatively easy. Although it can be tedious if you want to dive straight into making your next project. Nevertheless, this is a crucial step if you want to get the correct crochet hook size right for a project.
Patterns should specify the gauge for a project. Most commonly this the gauge will tell you how many stitches and rows you need to make in a particular stitch pattern in order to get a swatch that is 4″ x 4″ or roughly 10cm x 10cm.
The pattern should also recommend a hook size. If the hook size is given in the U.S. Size Range or Millimeter Range or vice versa, use the conversion chart to pick out the size of the hook that you have that is closest in size.
Make a swatch using the recommended hook and the yarn you have chosen. Measure the swatch.
If you get the right number of stitches and rows, you’re golden. You’ve found the correct size hook for your pattern based on your tension and yarn. Go ahead and start the pattern using that hook size.
If you have more stitches and rows than called for, you are crocheting tighter than is called for in the pattern. So, you need to use a bigger crochet hook. Go up a size to a different hook and try making the gauge swatch again. Keep doing this until you match the number of stitches and rows call for in the pattern gauge.
Similarly, if you have fewer stitches and rows than called for, you are crocheting looser than is called for in the pattern. So, you need to use a smaller crochet hook. Go down a size and try making the gauge swatch again. Keep adjusting until you make a number of stitches and rows that matches the pattern gauge.
Crochet Hooks for Various Yarn Weights
Yarns come in various weights which refers to the thickness of the yarn. You can find a guide to yarn weights in the standard yarn weight systempublished by the Craft Yarn Council. In this system, a bulky yarn will be much thicker/heavier than a lace yarn.
You can pick a particular hook for a particular yarn weight in several ways:
- Look at your pattern and use the recommended yarn weight with the recommended hook.
- Look at your yarn label. It should tell you the weight of your yarn and the recommended hook or range of hooks.
- Use the table below.
- Working a gauge swatch is the best way to identify the right hook for your pattern.
Here’s a rough guide to recommended crochet hooks for the various yarn weights.
Crochet Hook Sizes For Yarn Weights
| Yarn Weight | Other Name(s) for Yarn Weight | Millimeter Range Recommended Hooks | U.S. Size Range Recommended Hooks |
| Lace #0 | Light Fingering | 2.25 mm | B-1 |
| Super Fine #1 | Sock, Fingering, Baby | 2.25 to 3.5 mm | B-1 to E-4 |
| Fine #2 | Sport, Baby | 3.5 to 4.5 mm | E-4 to 7 |
| Light #3 | DK Yarn, Light Worsted | 4.5 to 5.5 mm | 7 to I-9 |
| Medium #4 | Worsted, Aran | 5.5 to 6.5 mm | I-9 to K-10 ½ |
| Bulky #5 | Chunky, Craft, Roving | 6.5 to 9 mm | K-10 ½ to M-13 |
| Super Bulky #6 | Super Bulky, Roving | 9 tp 15 mm | M-13 to Q |
| Jumbo #7 | Jumbo, Roving | 15 mm and larger | Q and larger |
Note: These are rough estimates only. Crocheting a gauge swatch is the best way to determine the appropriate hook to use. Patterns using lace weight yarns are particularly likely to call for different hooks sizes. A larger hook used with a lace weight yarn will produce openwork that is lacier.
Frequently Asked Questions
How many sizes of crochet hooks are there?
There are a wide variety of sizes of crochet hooks. Not only are there standard crochet hooks, but there are also steel crochet hooks sizes for thread and lace projects.
For standard crochet hooks, there are at least nineteen different hook sizes in the U.S. letter system. And there are at least twenty-nine different hook sizes in the metric system. This corresponds to at least thirteen different sizes in the old UK system.
This guide has covered six different crochet hook systems: (1) the metric or millimeter range system for standard hooks, (2) the metric system for steel hooks, (3) the U.S letter system, (4) the U.S. number system, (5) the old UK system for standard hooks sizes, and (6) the UK steel system for steel crochet hook sizes. And there are more!
Obviously for a craft as old and honored as crochet, there will be many different hook sizes and systems. This is history is part of what makes exploring crochet so fun. The key in the end is finding the right hook size for your project.
What letter is a 2.5 mm crochet hook?
There is no letter in the U.S. system for a 2.5 mm crochet hook. Try using a B-1 or a C-2 hook to make a gauge swatch. These hooks are the closest in size.
What size is a 3mm crochet hook?
There is no letter in the U.S. system for a 3mm crochet hook. Try using a C-2 or a D-3 hook to make a gauge swatch. These hooks are the closest in size.
What size is a g crochet hook?
A g crochet hook can either be 4.0 mm or 4.25 mm in size. Check the metric measurement on your hook to get the most precise measurement.
How many mm is a size h crochet hook?
A size H-8 crochet hook is 5.0 mm in size.
What is a 5.5 mm crochet hook?
A 5.5 mm crochet hook is an I-9 hook in the U.S. system.
What letter is a 7mm crochet hook?
A 7.00 mm hook is between a K-10 1/2 hook and an n hook. It would also be lower in size than an L-11 hook. However, an L-11 hook that is 8.00 mm is hard to find.
What size is an n crochet hook?
Because of the variations in the U.S. system, an n hook can be either 9.00 mm or 10.00 mm.
What is the largest crochet hook size?
According to Guinness World Records, the largest crochet hook is 11 cm (4.3 in) in diameter and 2.77 m (9 ft 1 in). This record was achieved on December 11, 2017.
The largest crochet hook I own is an S hook that is 19 mm. Here it is next to J hook for comparison.
Curious about how many yards are in 100 grams of a particular yarn? Check out this post. Looking for new hooks? This is a set of my favorite ergonomic crochet hooks.
