Knitting & crochet calculator
Needle & Hook Size Converter
Enter a US, UK/Canadian, or metric (mm) knitting needle or crochet hook size and get the equivalent sizes in the other two systems.
Knitting needles and crochet hooks are sized differently depending on where a pattern was published: US sizes use a number scale, UK and Canadian sizes use a reversed number scale (a bigger UK number means a smaller tool), and the rest of the world uses metric millimeters. This mismatch trips up a lot of knitters and crocheters working from patterns published outside their home region.
This converter uses the standard published size charts for both needles and hooks. Pick your tool type, choose the system your known size is in, and enter the value to see the equivalent sizes in the other two systems.
Worked example: a US size 7 knitting needle is a UK size 6, and measures 4.5mm.
Frequently Asked Questions
Why do UK needle sizes count down as US sizes count up?
The UK/Canadian system originated from wire gauge numbering, where a higher gauge number means a thinner wire. US sizing was set up later as a simpler ascending scale.
Is metric (mm) sizing more reliable than US or UK sizes?
Yes - millimeter sizing is the actual physical diameter of the needle or hook, so it's the most precise way to match sizes across brands and regions, especially since US/UK size numbers can vary very slightly by manufacturer.
Do crochet hooks and knitting needles use the same size chart?
No, they use separate size charts even though both reference the same three systems (US, UK/Canadian, metric). Always convert within the correct tool type.
What if my exact size isn't in the table?
Very old or specialty sizes sometimes fall outside the standard chart. The converter will show the nearest standard size when you search by millimeter.