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Knitting Needle Size Converter

A knitting needle size converter maps millimetres to US, UK, and Japan knitting numbers and to crochet hook letters. The millimetre column is the Craft Yarn Council standard; letter and number labels are the usual retail names for that millimetre.

Quick Summary & Direct Answer
Craft

What millimetre is a US 8 knitting needle?

A US 8 knitting needle is 5.0 mm. UK 6 is the same millimetre. A US H-8 crochet hook is also 5.0 mm. Japan 10 is listed on the same row. Always trust the millimetre stamp on the needle over a worn painted size.

Key Takeaways

  • Millimetres are the only column that is physically the shaft diameter.
  • US knitting numbers and crochet letters can share a millimetre.
  • UK sizes run the other way: smaller UK numbers are larger needles.
  • Japan sizes in this table follow common CYC-aligned charts.

4 mm

US knitting 6 · UK 8 · Japan 8

Crochet US G-6 · UK 8

Chart aligned with the Craft Yarn Council knitting needle sizes.

mmUS knitUKJapanCrochet USCrochet UK
2.000140—14
2.251131B-113
2.501.5122—12
2.752123C-212
3.002.5114—11
3.253105D-310
3.504—6E-49
3.75597F-59
4.00688G-68
4.5077977
5.008610H-86
5.509511I-95
6.0010412J-104
6.5010.5313K-10.53
7.00—214—2
8.0011015L-110
9.001300—M/N-1300
10.0015000—N/P-15000
12.0017——P/Q—
15.0019——Q—
19.0035——S—
25.0050————

Results can be wrong. This calculator is unofficial. Figures can be incomplete, rounded, or not updated. Use them at your own risk and check a tape, datasheet, ball band, or official chart before cutting, mixing, buying, or publishing. Limits of liability are in the terms of service.

Frequently asked questions

Both are 5.0 mm in the Craft Yarn Council chart. The tools are different, the shaft diameter is not.

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Publisher notes · reviewed 29 October 2026

Millimetres are the shaft; US and UK are labels

The millimetre column is Craft Yarn Council standard diameter. US numbers and crochet letters are retail names for that millimetre. UK numbers run the opposite direction. Gaps such as no UK size for 3.5 mm are shown as dashes.

When labels disagree

A worn painted US 8 that measures 4.8 mm is not 5.0 mm. Trust calipers over paint.

Worked examples

  • US 8

    5.0 mm, UK 6, crochet H-8.

Limits of this page

  • The chart does not convert gauge.
  • Japan numbers follow common CYC-aligned lists, not every domestic brand.

Sources