🧵 Knitting Needle Size Converter (US / UK / mm)

Convert between US, UK (old), and metric (mm) knitting needle sizes in one place.

mm (Metric)

—

US Size — mm (Metric) — UK (Old) Size —

Knitting Needle Size Conversion Table

US	mm	UK (Old)
0	2.0	14
1	2.25	13
2	2.75	12
3	3.25	10
4	3.5	—
5	3.75	9
6	4.0	8
7	4.5	7
8	5.0	6
9	5.5	5
10	6.0	4
10.5	6.5	3
11	8.0	0
13	9.0	00
15	10.0	000
17	12.75	—
19	15.0	—
35	19.0	—
36	20.0	—
50	25.0	—

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GUIDE

Learn more

Understanding Knitting Needle Size Systems

Knitting needle sizes are labeled differently depending on country and brand. US sizes use a numeric scale from 0 to 50. UK (old) sizes run in the opposite direction — a larger number means a thinner needle (this system is largely obsolete, replaced by metric). mm (metric) is the international standard indicating the needle's actual diameter. Vintage or overseas (especially UK/Australian) patterns may still list UK (old) sizes, which is when conversion becomes necessary.

The most reliable reference is always the mm diameter, since actual diameter can vary slightly by brand even at the "same" labeled size — for projects where gauge precision matters, measure with calipers or a needle gauge.

Knitting Needle Size Conversion Table

Below is the standard conversion table between US, metric (mm), and UK (old) knitting needle sizes. A dash ("—") means there is no standard equivalent in that system.

US	mm	UK (Old)
0	2.0	14
1	2.25	13
2	2.75	12
3	3.25	10
4	3.5	—
5	3.75	9
6	4.0	8
7	4.5	7
8	5.0	6
9	5.5	5
10	6.0	4
10.5	6.5	3
11	8.0	0
13	9.0	00
15	10.0	000
17	12.75	—
19	15.0	—
35	19.0	—
36	20.0	—
50	25.0	—

This table follows the standard knitting needle size conversion commonly published by the Craft Yarn Council and major yarn manufacturers.

Frequently asked questions

Why does a bigger UK (old) number mean a thinner needle?

The UK (old) system originated from numbered holes on a needle gauge plate, so it runs opposite to the modern US/mm systems — larger number, thinner needle. It has largely been replaced by metric sizing.

What do I do about sizes marked "—" in the table?

That means there is no standard equivalent defined in that sizing system. In that case, use the mm (metric) diameter as your reference, or buy needles labeled in mm for the most accurate match.

Do needles of the same US size vary in actual diameter by brand?

Slightly, yes. For projects where gauge precision matters, measure your needle's actual diameter with calipers or a needle gauge rather than relying on the labeled size alone.