When I started crocheting, I was so eager to jump in and start, I didn't realize that crochet hook sizing mattered in my projects. But it matters! So let me guide you to everything you need to know about crochet hook sizes.

Hook and size

Crochet hooks (somtimes called needles) are the tools we use for crocheting. They have a little hook at the end, which is used to grab and pull yarn to create the stitches. They come in all size and materials - I personally use a set of colorful hooks with ergonomic handles.

The hook size is determined by the diameter of the hook (the area between the handle and the hook) measured in millimeters. The size is usual in millimeters or US units (letters and numbers). Most often the hook size will be stated on the hook. If you hook doesn't have the size on it, you can buy a hook measurement tool.

Millimeters	US	UK
2.25 mm	B/1	13
2.75 mm	C/2	-
3.25 mm	D/3	10
3.50 mm	E/4	9
3.75 mm	F/5	-
4.00 mm	G/6	8
4.50 mm	-	7
5.00 mm	H/8	6
5.50 mm	I/9	5
6.00 mm	J/10	4
.6.50 mm	K/10.5	3
7.00 mm	-	-
8.00 mm	L/11	0
9.00 mm	M/13	00
10.00 mm	N/15	000

Choosing the right hook size

First off: Are you following a pattern? If you are; use whatever needle and yarn that are specified in the pattern. Using hook sizes that differs from what’s specified in the pattern, will make your product turn out differently than the original design - both in size and/or shape!

How much it varies and what impact it has depends on what you are crocheting. If it is a scarf or a blanket, a slight change in the hook size will not have a great impact. However, if it is items such as clothing that need to be correctly sized, using the right crochet hook is key.

If you do not follow a pattern, you want to match your crochet hook to your yarn weight. Super fine yarns require small hooks, while thicker yarns require larger hooks to achieve even stitches. The preferred hook size will be apparent from your yarn label.

When in doubt - test!

Using the crochet hook that is specified in the pattern will most often be the right choice - but to be sure, you can crochet a test swatch. This only works for patterns that specifies how many stitches will be pr. 10x10 cm or an inch-long.

Doing a test swatch means that you crochet a few rows of the stitches specified in the pattern. Then measure a 10x10 cm piece and count how many stitches you made across and how many rows lengthwise. If it matches the pattern, you're good. If you made fewer, you either have to use a smaller hook or crochet tighter. If you made too many stitches, you have to use a bigger hook or loosen your stitches.

I hope this guide helped you!