Needle & hook size converter

Knitting needle sizes

Craft Yarn Council chart, checked 22 October 2026. UK sizes are the legacy British system and are shown for reference only.

Metric	US	UK
1.5 mm	000	14
1.75 mm	00	—
2 mm	0	14
2.25 mm	1	13
2.75 mm	2	12
3 mm	—	11
3.125 mm	3	—
3.25 mm	3	10
3.5 mm	4	—
3.75 mm	5	9
4 mm	6	8
4.25 mm	6	—
4.5 mm	7	7
5 mm	8	6
5.25 mm	9	—
5.5 mm	9	5
5.75 mm	10	—
6 mm	10	4
6.5 mm	10.5	3
7 mm	—	2
7.5 mm	—	1
8 mm	11	0
9 mm	13	00
10 mm	15	000
12.5 mm	17	—
12.75 mm	17	—
15 mm	19	—
19 mm	35	—
25 mm	50	—
35 mm	70	—

Crochet hook sizes

Letter and number sizes vary by manufacturer. The CYC advises relying on the millimetre size printed on the package.

Metric	US
2.25 mm	B-1
2.5 mm	—
2.75 mm	C-2
3.125 mm	D
3.25 mm	D-3
3.5 mm	E-4
3.75 mm	F-5
4 mm	G-6
4.25 mm	G
4.5 mm	7
5 mm	H-8
5.25 mm	I
5.5 mm	I-9
5.75 mm	J
6 mm	J-10
6.5 mm	K-10.5
7 mm	—
8 mm	L-11
9 mm	M/N-13
10 mm	N/P-15
11.5 mm	P-16
12 mm	—
15 mm	P/Q
15.75 mm	Q
16 mm	Q
19 mm	S
25 mm	T/U/X
30 mm	T/X

Steel crochet hooks

Steel hooks are sized the opposite way to regular hooks: a higher number is a smaller hook. They are used with crochet thread and lace-weight yarn.

US steel size	Metric
14	0.9 mm
13	0.95 mm
12	1 mm
11	1.1 mm
10	1.15 mm
9	1.25 mm
8	1.3 mm
7	1.4 mm
6	1.5 mm
5	1.6 mm
4	1.75 mm
3	1.9 mm
2	2.1 mm
1	2.25 mm
0	2.5 mm
00	2.7 mm

Why millimetres win

There is no enforceable international standard for US needle numbers. A US 6 from one brand can measure 4.0 mm while another measures 4.25 mm. The CYC's own guidance is blunt: rely on the millimetre size, which is an accurate measurement.

This matters most when you are matching a gauge. A 0.25 mm difference is enough to shift a 20-stitch swatch by half a stitch, which becomes several centimetres across a sweater body.

A row of knitting needles and crochet hooks standing upright in increasing sizes — From lace to jumbo: the tool follows the yarn, not the label.

Questions

My pattern gives an old UK size. What do I do?

Convert it to millimetres with the table above, then swatch. UK sizes were never perfectly consistent, and vintage patterns often assume a different yarn than the one you are using.

Is a US 10.5 the same as a 10?

No. US 10.5 is 6.5 mm; US 10 is 6.0 mm. Half sizes exist precisely because 0.5 mm changes the fabric.

Why does my hook letter not match the chart?

Because letter sizing is not standardised. Trust the millimetre figure on the hook itself, and if the hook is unmarked, measure the shaft with calipers.

Source: Craft Yarn Council, Hooks & Needles and Steel Hooks & Crochet Threads. Checked 22 October 2026.