The thickness of yarn is known as its weight and there are standard symbols, names and a numbering system that can help you understand how thick a yarn is and what thickness yarn is required for a pattern. This information can usually be found on the ball band on yarn and at the start of knitting and crochet patterns. Below we have provided a helpful table that will help you see what needle or hook size you need for a given yarn. This is especially helpful if you are buying yarn online and want to get an idea of how thick it is.
Standard Yarn Weight  | 
0  | 
1  | 
2  | 
3  | 
4  | 
5  | 
6  | 
7  | 
UK Yarn Type  | 
Lace  | 
3 or 4 Ply  | 
4 Ply  | 
Double Knit (DK)  | 
Aran  | 
Chunky  | 
Super Chunky  | 
Roving  | 
US Yarn Type  | 
Lace  | 
Superfine, Sock or Fingering  | 
Fine, Sport or Baby  | 
Light or Worsted  | 
Medium, Worsted or Afghan  | 
Bulky, Craft or Rug  | 
Super Bulky or Roving  | 
Jumbo  | 
Australian Yarn Type  | 
2 Ply  | 
3 or 4 Ply  | 
4 or 5 Ply  | 
8 Ply  | 
10 Ply  | 
12-14 Ply  | 
16 Ply  | 
-  | 
Meters per 100gm  | 
600— 1100  | 
420—580  | 
260—400  | 
210—250  | 
130—200  | 
90—120  | 
40—80  | 
-  | 
Type of Yarns in Category  | 
Fingering 10-count crochet thread  | 
Sock, Fingering, Baby  | 
Sport, Baby  | 
DK, Light Worsted  | 
Worsted, Afghan, Aran  | 
Chunky, Craft, Rug  | 
Super Bulky, Roving  | 
Jumbo, Roving  | 
Knitting tension - 10cm - stocking stitch  | 
33–40 sts  | 
27–32 sts  | 
23–26 sts  | 
21–24 sts  | 
16–20 sts  | 
12–15 sts  | 
7–11 sts  | 
6 sts and fewer  | 
Recommended knitting needle size  | 
1.5–2.25 mm  | 
2.25— 3.25 mm  | 
3.25— 3.75 mm  | 
3.75— 4.5 mm  | 
4.5— 5.5 mm  | 
5.5— 8 mm  | 
8— 12.75 mm  | 
12.75 mm and larger  | 
Crochet tension 10cm - double crochet  | 
32–42 double crochet  | 
21–32 sts  | 
16–20 sts  | 
12–17 sts  | 
11–14 sts  | 
8–11 sts  | 
7–9 sts  | 
6 sts and fewer  | 
Recommended crochet hook size  | 
Regular hook 2.25 mm  | 
2.25— 3.5 mm  | 
3.5— 4.5 mm  | 
4.5— 5.5 mm  | 
5.5— 6.5 mm  | 
6.5— 9 mm  | 
9— 15 mm  | 
15 mm and larger  |