If you are using older patterns handed down in the family or found in thrift store, you may be confused by the yarn sizes called for in them. Since most of the yarns old patterns reference are probably not made anymore, you will have to find a modern equivalent. A good way to judge is by the size of crochet hook the pattern calls for. Just find a modern yarn that is rated for the same size hook as all the current yarns will have a suggested hook size on the packaging.
Here is a handy chart of yarn numbers with the conversion to the old style names:
0 – Fingering, thread
1 – Sock, fingering, baby
2 – Sport, baby
3 – DK, double knit, light or light worsted
4 – Worsted, Aran, afghan, medium
5 – Chunky, bulky, craft, rug
6 – Super bulky, super chunky, roving
7 – Jumbo, roving
Note that there can be several names for the same size and that there will be variations in size for yarn rated the same number. Generally a #4 yarn will be fine with a G, H, or I hook but for the rest it is best to read the label for the suggested hook size. It is always safe to go up to the next size, you will just get a looser weave in the final product, but if you use a too small hook you will get a very stiff final product from the weave being too tight.
Another chart you may need is for the various ways hook sizes can be named. I grew up using the letter system in the US, but newer yarns or patterns now seem to lean toward giving a size in millimeters (mm). Here are the letter sizes with their corresponding US number, size in mm and UK number:
B — 1 — 2.00mm — 14
C — 2 — 2.50mm — 12
D — 3 — 3.25mm — 10
E — 4 — 3.50mm — 9
F — 5 — 3.75mm — n/a
G — 6 — 4.00mm — 8
H — 8 — 5.00mm — 6
I — 9 — 5.50mm — 5
J — 10 — 6.00mm — 4
K — 10.5 — 6.50mm — 3
This only covers the main hook sizes, and not the smaller steel hooks for thread. You can view an expanded chart that includes the steel hooks and more sizes at AllFreeCrochet.com
Crochet with Cindy 