Is a G hook 4 mm or 4.25 mm?

The standard G-6 is 4 mm, but some brands have labeled a 4.25 mm hook as "G." Use the millimeter size to be sure.

Why does the converter say "varies" for some UK sizes?

Published charts disagree about old UK sizes 12, 9 and 7. Rather than guess, we show "varies." Match by millimeters and check your gauge.

What hook should I use for worsted yarn?

The Craft Yarn Council recommends 5.5–6.5 mm (I-9 to K-10½) for medium yarn, though many crocheters use 5 mm (H-8) for a firmer fabric.

Gauge & Stitch

Crochet Hook Size Converter

Look up any crochet hook in millimeters, US letters and old UK numbers, and see which yarn weight it usually pairs with.

Crochet Hook Size Converter & Gauge Table

Instant conversions across Metric (mm), US letters, and UK vintage numbering

Active Selection

5.00 mm

US: H-8

UK / Old Size: 6 | Best for: 3 - Light (DK)

Hook Diameter Visualizer5 mm

Relative to 19mm Jumbo hook

Most Common Hook Sizes (Click to select):

Metric (Exact mm)	US Letter / Number	UK / Vintage	Standard Yarn Match	Action
2.00 mm	-	14	0 - Lace	Select
2.25 mm	B-1	13	0 - Lace / 1 - Super Fine	Select
2.50 mm	-	12 (varies)	1 - Super Fine	Select
2.75 mm	C-2	12 (varies)	1 - Super Fine	Select
3.00 mm	-	11	1 - Super Fine	Select
3.25 mm	D-3	10	1 - Super Fine	Select
3.50 mm	E-4	9 (varies)	1 - Super Fine / 2 - Fine	Select
3.75 mm	F-5	9 (varies)	2 - Fine	Select
4.00 mm	G-6	8	2 - Fine	Select
4.25 mm	G	-	2 - Fine	Select
4.50 mm	7	7 (varies)	2 - Fine / 3 - Light	Select
5.00 mm	H-8	6	3 - Light (DK)	Selected
5.50 mm	I-9	5	3 - Light / 4 - Medium	Select
6.00 mm	J-10	4	4 - Medium (Worsted)	Select
6.50 mm	K-10½	3	4 - Medium / 5 - Bulky	Select
7.00 mm	-	2	5 - Bulky	Select
8.00 mm	L-11	0	5 - Bulky	Select
9.00 mm	M/N-13	00	5 - Bulky / 6 - Super Bulky	Select
10.00 mm	N/P-15	000	6 - Super Bulky	Select
11.50 mm	P-16	-	6 - Super Bulky	Select
15.00 mm	P/Q	-	6 - Super Bulky / 7 - Jumbo	Select
16.00 mm	Q	-	7 - Jumbo	Select
19.00 mm	S	-	7 - Jumbo	Select
25.00 mm	T/U/X	-	7 - Jumbo	Select

Hook Sizing Warning: Always check the exact millimeter (mm) stamp on your hook! US letter sizes vary slightly between manufacturers (for example, some brands label a 4.5mm hook as G-7, while others label it simply 7). The millimeter diameter never lies.

A set of colored crochet hooks beside a skein of grey yarn

How to use the hook size converter

Row 1Search for a hook by millimeters (for example 5), a US size (for example H-8) or an old UK number (for example 6).
Row 2Or tap one of the common sizes to jump straight to it.
Row 3Read the matching sizes in the other systems, and the yarn weight that hook is typically used with.
Row 4If your pattern gives only a letter, use the millimeter size shown here when buying a hook.

Why millimeters are the size to trust

Hooks are labeled three different ways. Millimeters measure the shaft's diameter directly, which is what decides your stitch size. US letters were mapped to those millimeter sizes, and a few letters have been used for two slightly different hooks: "G" has meant both 4 mm and 4.25 mm. Old UK numbers were never fully standardized.

So the converter treats millimeters as the anchor. US sizes follow the Craft Yarn Council's hook chart. Where published charts disagree about an old UK size (UK 12, 9 and 7), the converter marks it "varies" rather than guessing.

Which hook for which yarn

Each hook in the converter is matched to the yarn weights the Craft Yarn Council recommends it for. For example, a 5.5 mm (I-9) hook sits where light (DK) and medium (worsted) yarn overlap.

Treat that as a starting point. Many crocheters use a 5 mm (H-8) hook with worsted yarn for a firmer fabric, amigurumi makers often go one or two sizes smaller, and lace often uses a larger hook. The hook that matches your pattern's gauge is always the right one. See our hook size guide for the full chart and more detail.

Tips

Check that the millimeter size is printed on any hook you buy. Labels get lost; the hook stays.
Following a vintage UK pattern? Use the millimeter equivalent and check your gauge, since old UK sizes vary.
Steel hooks for thread use a separate numbering system in which higher numbers are smaller hooks.
Changing hook size by half a millimeter is usually enough to correct your gauge.

Crochet Hook Size Converter FAQ

A 5 mm hook is a US H-8 (old UK size 6).

In-depth guides

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Gauge & Stitch

Crochet Gauge Calculator

Calculate stitch density and precise rows and stitches needed for your target project dimensions.

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Yarn Weight Converter

Compare Craft Yarn Council categories (0 to 7), WPI, ply equivalents (US/UK/AUS), and hook pairings.

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Stitch Count Calculator

Calculate the exact number of stitches needed to resize any pattern or match custom dimensions.

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Metric (Exact mm)

US Letter / Number

UK / Vintage

Standard Yarn Match

Action

2.00 mm

0 - Lace

Select

2.25 mm

B-1

0 - Lace / 1 - Super Fine

Select

2.50 mm

12 (varies)

1 - Super Fine

Select

2.75 mm

C-2

12 (varies)

1 - Super Fine

Select

3.00 mm

1 - Super Fine

Select

3.25 mm

D-3

1 - Super Fine

Select

3.50 mm

E-4

9 (varies)

1 - Super Fine / 2 - Fine

Select

3.75 mm

F-5

9 (varies)

2 - Fine

Select

4.00 mm

G-6

2 - Fine

Select

4.25 mm

2 - Fine

Select

4.50 mm

7 (varies)

2 - Fine / 3 - Light

Select

5.00 mm

H-8

3 - Light (DK)

Selected

5.50 mm

I-9

3 - Light / 4 - Medium

Select

6.00 mm

J-10

4 - Medium (Worsted)

Select

6.50 mm

K-10½

4 - Medium / 5 - Bulky

Select

7.00 mm

5 - Bulky

Select

8.00 mm

L-11

5 - Bulky

Select

9.00 mm

M/N-13

5 - Bulky / 6 - Super Bulky

Select

10.00 mm

N/P-15

000

6 - Super Bulky

Select

11.50 mm

P-16

6 - Super Bulky

Select

15.00 mm

P/Q

6 - Super Bulky / 7 - Jumbo

Select

16.00 mm

7 - Jumbo

Select

19.00 mm

7 - Jumbo

Select

25.00 mm

T/U/X

7 - Jumbo

Select

How to use the hook size converter

Row 1Search for a hook by millimeters (for example 5), a US size (for example H-8) or an old UK number (for example 6).

Row 2Or tap one of the common sizes to jump straight to it.

Row 3Read the matching sizes in the other systems, and the yarn weight that hook is typically used with.

Row 4If your pattern gives only a letter, use the millimeter size shown here when buying a hook.

Why millimeters are the size to trust

Which hook for which yarn

Each hook in the converter is matched to the yarn weights the Craft Yarn Council recommends it for. For example, a 5.5 mm (I-9) hook sits where light (DK) and medium (worsted) yarn overlap.

Tips

Check that the millimeter size is printed on any hook you buy. Labels get lost; the hook stays.

Following a vintage UK pattern? Use the millimeter equivalent and check your gauge, since old UK sizes vary.

Steel hooks for thread use a separate numbering system in which higher numbers are smaller hooks.

Changing hook size by half a millimeter is usually enough to correct your gauge.

Crochet Hook Size Converter

Crochet Hook Size Converter & Gauge Table

5.00 mm

How to use the hook size converter

Why millimeters are the size to trust

Which hook for which yarn

Tips

Crochet Hook Size Converter FAQ

In-depth guides

Crochet Hook Sizes Chart: mm, US Letters and UK Sizes Explained

US vs UK Crochet Terms: Conversion Chart and How to Tell Them Apart

Related Crochet Calculators & Converters

Crochet Gauge Calculator

Yarn Weight Converter

Stitch Count Calculator

Crochet Hook Size Converter

Crochet Hook Size Converter & Gauge Table

5.00 mm

How to use the hook size converter

Why millimeters are the size to trust

Which hook for which yarn

Tips

Crochet Hook Size Converter FAQ

In-depth guides

Crochet Hook Sizes Chart: mm, US Letters and UK Sizes Explained

US vs UK Crochet Terms: Conversion Chart and How to Tell Them Apart

Related Crochet Calculators & Converters

Crochet Gauge Calculator

Yarn Weight Converter

Stitch Count Calculator