4 mm knitting needles are equivalent to a US size 6 and a UK size 8.

Quick Scoop

  • Metric size: 4 mm
  • US size: 6
  • UK/Old UK size: 8

Here’s the same info in table form:

System Needle size for 4 mm
Metric 4 mm
US 6
UK 8
If a pattern says “US 6 (4 mm)” or “UK 8 (4 mm)”, they all mean the same needle thickness.