Crochet Hook Size Chart

Every crochet hook size, converted between millimetres, US letters and UK numbers, with the yarn weight each one suits. Buy on the millimetre size. A UK 9 is 3.5 mm and a US 9 is 5.5 mm — the two systems run in opposite directions, and that single fact is behind most wrong-hook purchases.

Metric	UK / Canada	US	Yarn weight	Typically used for
2.25 mm	13	B/1	Lace, thread	Fine amigurumi, doilies
2.50 mm	12	—	Lace, fingering	Tight amigurumi
2.75 mm	12	C/2	Fingering, sock	Amigurumi in fingering
3.00 mm	11	—	Sport	Small toys
3.25 mm	10	D/3	Sport, DK	Amigurumi in worsted — the usual choice
3.50 mm	9	E/4	DK	Amigurumi, dense fabric
3.75 mm	—	F/5	DK, light worsted	Small garments
4.00 mm	8	G/6	DK, worsted	Blankets, hats
4.50 mm	7	7	Worsted	Blankets, garments
5.00 mm	6	H/8	Worsted	Blankets, bags
5.50 mm	5	I/9	Worsted, Aran	Bags, baskets
6.00 mm	4	J/10	Aran	Chunky blankets
6.50 mm	3	K/10.5	Aran, bulky	Rugs, baskets
7.00 mm	2	—	Bulky	Fast blankets
8.00 mm	0	L/11	Bulky	Chunky throws
9.00 mm	00	M/13	Super bulky	Rugs, giant stitches
10.00 mm	000	N/15	Super bulky	Arm-scale work
12.00 mm	—	O	Jumbo	Giant blankets
15.00 mm	—	P/Q	Jumbo	Extreme chunky
20.00 mm	—	S	Jumbo, roving	Bulky rugs

Manufacturers disagree on the letters. One brand’s H is 5.0 mm, another’s is 5.25 mm. The millimetre figure stamped on the shaft is the only number that means the same thing in every country and every brand. If a pattern gives only a letter, convert it here and then check your hook’s stamp.

Which hook for amigurumi

3.25 mm with worsted yarn. That is deliberately one or two sizes below what the yarn label recommends, and the reason is structural: amigurumi has to be dense enough that the stuffing cannot show between the stitches. A 5.0 mm hook in worsted makes lovely drapey fabric and a toy you can see the filling through.

The same logic applies at every weight — for anything stuffed, go down from the label. For blankets and garments, follow it.

Why UK and US sizes run backwards to each other

US sizes use letters and numbers that get later and higher as the hook gets bigger: B/1, C/2, D/3 … N/15. UK and Canadian sizes use numbers that get smaller as the hook gets bigger: 14 is tiny, 000 is huge. They were never designed to align.

So a pattern that says “size 9” is ambiguous unless you know where it was written. A UK 9 is 3.5 mm. A US 9 is 5.5 mm. That is nearly two hook sizes apart and enough to ruin the fit of a garment.

How much does one size change your gauge

Roughly five to seven per cent per half-millimetre step. If your swatch comes out fifteen per cent tighter than the pattern, that is two sizes up, not one. The crochet gauge calculator works out the exact number from your swatch.

Frequently asked questions

What is a 3.5 mm crochet hook in US sizes?: A US E/4, and a UK 9. It suits DK yarn and dense amigurumi.
What is the most useful hook size to own?: 5.0 mm (US H/8) for flat work in worsted, and 3.25 mm (US D/3) for amigurumi in the same yarn. Those two cover most patterns you will meet in the first year.
What hook size is best for amigurumi?: 3.25 mm with worsted. Smaller than the label says, on purpose, so the stuffing stays hidden.
Why do US and UK hook sizes disagree?: Two separate historical systems running in opposite directions. Always convert to millimetres.
Does the hook size on the yarn label matter?: For garments and blankets, yes — follow it. For toys, go one or two sizes below it.
Are steel hooks measured differently?: Yes. Steel hooks for thread use their own numbering where higher numbers are smaller — a steel 14 is about 0.9 mm. Do not read steel sizes against the aluminium chart above.

Related free tools

Yarn weight chart — identify any yarn from its label ·
Crochet gauge calculator — how many sizes to move ·
Yarn yardage calculator — grams to yards ·
Crochet increase calculator ·
All free craft tools

Our crochet patterns state the hook in millimetres and the yarn weight on the first page, so there is nothing to convert before you start. Over 150 patterns from $1.99.