G crochet hook: G-6 is 4 mm

A US size G-6 crochet hook is 4 mm at most brands. Turned around: a hook stamped 4 mm is usually sold as a G. In the old UK numbering it is an 8.

The letter and the number are one hook, not two — “G-6” is a single size. Older hooks often print only one of the pair, which is most of the confusion. The millimeter is stamped on the hook itself, so when a pattern and a label disagree, trust the mm.

What yarn this hook is for

4 mm falls in the hook range the Craft Yarn Council suggests for one yarn weight — guidelines, in their own words, not rules:

• Fine (2) — also sold as Sport, Baby. Expect about 16–20 single crochet to 4 inches.

Before you trust the letter

The Craft Yarn Council puts it plainly: “Because letter and number sizing vary from company to company, rely on the package millimeter (mm) sizing, which is an accurate measurement.” Only E (3.5 mm) and H (5 mm) mean the same thing at every brand — a hook stamped G is 4 mm from Susan Bates or Clover and 4.25 mm from Boye, and from L upward the letters drift far enough that the Council stops printing single ones.

This size in particular: Susan Bates, Clover and Furls call this a G-6. Boye stamps G on a 4.25 mm hook instead, and Addi on a 4.5 mm. If a pattern was written for a G, check the mm on your own hook.

The UK number is history rather than shopping: British hooks have been sold in millimeters since the 1970s, and these numbers turn up in vintage patterns and on inherited hooks. Watch one trap — UK crochet hooks and UK knitting needles are numbered differently below 4 mm, and a great many charts online quietly print the needle ladder for hooks. Vintage steel thread hooks used a third scale again.

The sizes either side

• One size down: F-5 — 3.75 mm
• One size up: 4.25 mm

Half a millimeter is enough to change how a finished piece comes out. If your gauge is off, this is the dial to turn before you change anything in the pattern — the gauge calculator says which way to go.

See every hook size in one chart →