If you’ve ever walked down the yarn aisle or browsed online for crochet supplies, you’ve probably noticed that crochet hooks come in a wide range of sizes—letters, numbers, millimeters… what does it all mean?

Whether you’re brand new to crochet or just looking to better understand your tools, this guide breaks down everything you need to know about crochet hook sizes, so you can confidently choose the right one for your project.

What Do Crochet Hook Sizes Mean?

Crochet hook sizes refer to the diameter of the hook’s shaft, which determines how big your stitches will be. A smaller hook makes tighter, smaller stitches; a larger hook makes looser, bigger stitches.

Hook sizes are labeled in three main ways:

• US Sizes: Letters (like B, G, K) and/or numbers (like 6, 10.5)
• Metric Sizes: Millimeters (mm) – the most precise measurement
• UK/Canadian Sizes: Different numbering system (less commonly used today)

📏 US vs. Metric Crochet Hook Sizes

Here’s a quick comparison chart for common hook sizes:

Note: Not all brands label their hooks the same way—always check the mm size when in doubt!

🧶 How to Choose the Right Hook Size

The best hook size depends on:

• The yarn weight: Yarn labels usually recommend a hook size.
• Your pattern: Most patterns list the hook size used.
• Your personal tension: If you crochet tightly or loosely, you may need to adjust.

📝 Tip: Always make a gauge swatch when following a pattern, especially for garments, to ensure your stitches match the designer’s tension.

🎯 What Happens If You Use the “Wrong” Size?

Using a smaller hook than recommended will make your project:

• Tighter
• Denser
• Smaller than expected

Using a larger hook than recommended will make your project:

• Looser
• More open or lacy
• Larger than expected

This isn’t always bad! You can use this intentionally to change the look or drape of a project—just be mindful if size matters (like with garments or hats).

So What Size Hook Should Beginners Start With?

If you’re just starting out, I recommend:

• Hook size: H-8 (5.0 mm) or I-9 (5.5 mm)
• Yarn: Worsted weight (category 4)

This combo is easy to work with and helps you clearly see your stitches while learning.

Final Thoughts

Crochet hook sizes might seem confusing at first, but once you understand the basics, choosing the right size becomes second nature. Whether you’re following a pattern or experimenting with your own designs, the hook you use makes a big difference in the look and feel of your finished piece.