Knitting needle sizes old and new: everything you need to know.
What are old UK sizes?
As you can see from the conversion chart below, the larger the needle, the smaller the size of needle. If you have inherited any Aero knitting needles from an older friend or relative, they might be size 8s or size 10s. Generally speaking, in most 20th century knitting bags, you'd find 10 for the ribbing (3.25mm) and 8 for the body of the DK weight garment. You are more likely to find 9s and 11s in there too, because 4ply used to be the most common yarn weight out there.
What are US needle sizes?
US needle sizes go up in size to correspond with the thickness of the needle, which is logical when looking at it. They start at 0 (2mm) and scale up to 15 (10mm).
Vintage patterns and old UK needles:
If you are working with vintage patterns you will see that they ask for the old UK size needles. You will need to know what the modern equivalent is in today's needles in order to even work up a swatch!
With the metric system being the most used system in the world, knitting patterns now state metric size knitting needles on their materials list. All international manufacturers of knitting needles and crochet hooks use the metric system on their products,
Fun fact: Only three countries in the world have yet to adopt the metric system:
As for everyone else, there is wide recognition of millimetres when looking at needle sizes. You will still see "4mm/ US 6" or "4mm/UK 8" on some patterns, but broadly speaking, metric is the most used today among knitters.
Here is an ad free knitting needle conversion chart.
Nowadays, knitting needles come in so many shapes and sizes that this chart will be just the beginning of your needle conversion. Any vintage pattern I have ever used gives instructions for a flat knit piece, but did you know that you can knit straight on circular needles too?
Here are the three main types of needle that you will see: