Knitting Needle Size Converter
Convert knitting needle sizes between the US system, metric millimeters and the old UK/Canadian numbering.
How to use the Knitting Needle Size Converter
- Choose the system you know.
- Enter the size (e.g. 8, 5 or 6).
- Read the equivalents.
How it works
The metric size is the needle’s diameter in millimeters and is the most accurate. US sizes increase with diameter (US 8 = 5 mm), while the old UK and Canadian system runs the opposite way — larger numbers are thinner (UK 6 = 5 mm). Patterns usually list a needle size and gauge; always knit a swatch, as gauge matters more than needle size.
Frequently asked questions
What is a US 8 needle in mm?
5 mm.
What size is a 4 mm needle in US?
US 6.
Why do UK sizes go backwards?
They were based on wire gauge, where higher numbers are thinner.
What needle size for worsted yarn?
Usually US 7–9 (4.5–5.5 mm).