Millimeters are the hook’s true size; letters and numbers are labels stamped on top, and steel thread hooks run backwards. Enter any size in any system; the rest come back, with the yarn that hook usually works.
Convert a Size
Type a number like 5, or a letter like H.
That Hook Is
H-8
5 mm · US H-8 · works worsted
- Millimeters5 mm
- US sizeH-8
- Usually worksworsted
How the Systems Relate
mm is the measurement · US letters climb with size · steel numbers fall as hooks growRegular hooks run B through S for yarn; steel hooks run 00 down to 14 for thread, and bigger number means smaller hook. When a vintage pattern says “size 7 hook”, the thread weight tells you which system it meant.
The Full Chart
| mm | US | Usually works |
|---|---|---|
| 2.25 | B-1 | fingering |
| 2.75 | C-2 | fingering |
| 3.25 | D-3 | sport |
| 3.5 | E-4 | sport |
| 3.75 | F-5 | sport–DK |
| 4 | G-6 | DK |
| 4.5 | 7 | DK |
| 5 | H-8 | worsted |
| 5.5 | I-9 | worsted |
| 6 | J-10 | worsted–bulky |
| 6.5 | K-10½ | bulky |
| 8 | L-11 | bulky |
| 9 | M-13 | super bulky |
| 10 | N-15 | super bulky |
| 12 | P-16 | super bulky |
| 15 | P/Q | jumbo |
| 16 | Q | jumbo |
| 19 | S | jumbo |
Steel Thread Hooks
| Steel US | mm | Steel US | mm |
|---|---|---|---|
| 4 | 2.00 | 11 | 1.10 |
| 5 | 1.90 | 12 | 1.00 |
| 6 | 1.75 | 13 | 0.85 |
| 7 | 1.65 | 14 | 0.75 |
| 8 | 1.50 | 16 | 0.60 |
| 10 | 1.25 | 18 | 0.50 |
Steel hooks work crochet thread and lace. A steel 7 (1.65 mm) and a regular US 7 (4.5 mm) are different tools three sizes of yarn apart.
Reading a Pattern’s Hook Size
- Trust the millimeter when the hook lists both: letters drift between brands (a vintage Boye K is not a Susan Bates K), millimeters never do.
- Thread patterns mean steel. Doilies, filet, and bedspread cotton call their hooks by steel numbers; the thread size (10, 20, 30) climbs finer alongside them.
- The label’s hook is a starting point: your gauge swatch picks the final size, usually within one hook either way.
Hook Size Questions, Answered
What size is an H crochet hook?
An H crochet hook, labeled H-8, is 5 mm, the everyday worsted hook and the one most beginner patterns mean. The letter and the number name the same hook, and the millimeter measurement is what both of them stand for.
What do the letters on crochet hooks mean?
The letters on crochet hooks are an American sizing ladder from B (2.25 mm) up to S (19 mm), so a later letter means a thicker hook. Most letters also carry a paired number, as in H-8 or K-10½, left over from an older numbering system, and both name the same size.
What crochet hook size should I use for my yarn?
The usual hook sizes by yarn weight are B to E for fingering, G to 7 for DK, H to I for worsted, K to L for bulky, and M and up for super bulky. The ball band prints the hook the mill used for its swatch, so start there and let your gauge swatch confirm it.
Why does my vintage crochet pattern’s hook seem tiny?
A vintage pattern’s hook seems tiny because it is a steel hook size: a 1950s doily pattern calling for a No. 7 hook means steel 7, which is 1.65 mm and meant for thread. A modern 4.5 mm hook with the same number would triple the doily’s size, because steel numbers grow larger as the hooks grow smaller.