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knitting needles

Knitting needles are selected for color (which should contrast with the color of the yarn being knit), length, and size number, the latter indicating the needle's diameter. Choosing the right size number for a project is crucial, because the diameter of the needles is one of the factors that determines the size of the garment.

Unfortunately, needles from different manufacturers that are supposedly the same size may have different diameters. If you must change needles in the middle of a project, compare the actual diameters of the old and new needles; don't simply rely on their sizes.

The table below shows the American size numbers with a range of actual diameters that might be encountered. It also shows the standard metric sizes (which are simply the needle’s diameter in millimeters) and their equivalents in the old United Kingdom sizes. To compare metric or old United Kingdom sizes with American sizes, compare the metric size with the American diameter in millimeters.

In knitting, the word “gauge” has a special meaning, the number of stitches in 1½ inches, and so to avoid confusion, we will not refer to knitting needles’ size numbers as a gauge.

Single-pointed Needles. Sizes range from 0000 to 50, with smaller numbers representing thinner needles.

Aluminum needles come in lengths of 7″, 10″, 12″, and 14″, and size numbers of 0 to 5 in the short lengths and 0 to 8 in the longer.
Plastic needles are made in sizes 0 to 10½, 13, and 15. Wooden needles are 14 inches long in sizes 10 to 15.
Steel needles are now only available in the smaller sizes, 0 to 3.

Double-pointed Needles. Double-pointed needles are made in even inch lengths of 5″, 6″, 7″, 10″, and 14″. The sizing of double-pointed needles varies with the material from which the needles are made. Plastic needles run from 1 through 10, from fine to thick. In contrast, steel double-pointed needles run from 18 to 8, with the highest number being the thinnest needle. For aluminum needles, some manufacturers use the plastic system and some the steel.

Circular Needles. Circular needles consist of two solid needles joined by a flexible cord. The solid needles are made of bamboo, wood or metal and are sized the same way single-pointed needles are. The smallest sizes, 0 through 3, are usually made of steel. In addition to the size of the needles, the sizes of circular needles also include a length, typically 29 inches or 80 cm, but circular needles with lengths of 16″, 20″, 24″ and 32″ are also made. A typical size would be “15 (10mm) by 29 inches.” The length is the distance from needle tip to needle tip, not the length of the cord.

In the process of converting to metric diameters, the sizes were adjusted slightly. Shaded boxes in the metric column indicate real metric sizes; the others are the equivalent in millimeters to the sizes in other systems.

Knitting Needle Sizes
United States			Metric (mm)	Old UK, Australia, etc.	Japan
Size	Observed diameter in millimeters	Steel double- pointed	Metric (mm)	Old UK, Australia, etc.	Japan
0000	1.25		1.25	16
000	1.5–1.75	15	1.5	15
00	1.75–2	14	2	14
0	2.1–2.25	13	2.1		0
1	2.25–2.75	12	2.25	13
			2.4		1
2	2.75–2.8–3	11	2.75	12	2
			3	11	3
3	3–3.3		3.125
		10	3.25	10
			3.3		4
4	3.5–3.75	9	3.5
			3.6		5
5	3.75–3.8–4	8	3.75	9
			3.9		6
			4	8
			4.2		7
6	4–4.25–4.5		4.25
7	4.5–4.6		4.5	7	8
			4.8		9
8	5.0		5	6
			5.1		10
9	5.3–5.5		5.25
			5.4		11
			5.5	5
			5.7		12
10	5.75–6		5.75
			6	4	13
			6.3		14
10½	6.5–7		6.5	3
			6.6		15
			7	2	7mm
			7.5	1
11	8.0		8	0	8mm
13	9–9.2–10		9	00
15	10–10.2		10	000
16
17	12.7		12.50
			12.75
18	14.3
19	16.0		15
35	19.0		19
50	25.4		25

resources

https://www.yarnstandards.com