The bigger the needle, the better, right? Not so fast! Every needle size (and type) has its purpose. And not only that, once you narrow down the size, there's the material and type to consider, too. With so many choices, it can be really hard to decode which needles to use for each project. Consider this your cheat sheet!


Sizing Conventions

First things first: knitting needles come in sizes. And those sizes are numbered: the smaller the number, the smaller the needle (and the thinner the yarn you'll use).

Needles in South Africa are using the metric system. Needles in the USA will often list both the US size and the metric size. Make sure you're you know which number is which, because a US 7 and 7 mm are NOT the same size. And, just to make things more confusing, you may also see UK sizes, which run in the opposite direction (the higher the number, the smaller the needle). All the sizes listed in this article refer to metric sizes.


KNITTING NEEDLE CONVERSION CHART

Metric (mm)
US
UK/Canada
2.0
0
14
2.25
1
13
2.75
2
12
3.0
11
3.25
3
10
3.5
4
3.75
5
9
4.0
6
8
4.5
7
7
5.0
8
6
5.5
9
5
6.0
10
4
6.5
10 1/2
3
7.0
2
7.5
1
8.0
11
0
9.0
13
00
10.0
15
000
12.0
17
16.0
19
19.0
35
25.0
50


Your project will dictate what size needle you use. Working from a pattern? It will suggest a needle size, and that's a good place to start (sure, your gauge could be off and you may need a different needle size to compensate, but that's a discussion for another day). Or, you may fall in love with a yarn, and decide you just have to knit with it. If you know the weight of your yarn, it's not hard to figure out what size needle to use. In fact, yarn labels often call out needle sizes right on the label. Easy peasy.


Materials

Knitting needles are generally made out of wood (primarily bamboo) or metal (primarily aluminum, but some other metals, too). Plastic needles are also out there, as are custom-made needles.

Which material you choose really comes down to personal preference, though there are some considerations based on size, too (more on that below). Many beginners prefer bamboo needles, because the wood causes a bit of drag on the stitches, and things are less likely to slip off unintentionally. Metal needles tend to be a bit slipperier, but are great if you want those stitches to fly off your needles.


Straight, Circular or DPNs

Here's a secret: you can use a circular needle to ANYTHING. Flat, in the round, small circumference, large circumference: it does it all. When in doubt, grab a circular needle with cord at least 36" long, and you're good to go. (Quick shout out to the interchangeable circular needle set: you can mix and match your needle tips with different cord lengths to give you all the options.)

Of course, not everyone loves circular needles, which is fine! If you prefer double-pointed needles (DPNs), you do you. One isn't better than another, promise.

And now, onto the sizes. And if you just love straight needles, then use them for alllll your flat projects.


Knitting Needle Sizes up to 2.25mm

These are the itty-bitty needles of the knitting world. If you're a true beginner, you can ignore these. They're generally used for intricate lace projects or projects that require intense amounts of patience. In fact, finding needles this small can sometimes be a challenge. They're a bit specialized.


Knitting Needle Sizes 2.25mm - 3.25mm

This needle size has a big claim to fame: socks! Cozy socks are one of the big perks of being (or knowing!) a knitter, and making them is kind of addicting. Most socks are knit using a 2.25mm or 2.75mm needle and use sock yarn, but you can also find patterns that are designed for heavier non-sock yarns. In addition to socks, you can knit up beautiful shawls using sock-weight yarn and these small needles.


Knitting Needle Sizes 3.25mm - 3.75mm

We're in sport-weight territory now. While not as thin as sock yarn, sport-weight yarn still uses somewhat thin needles. Sport-weight can be used for all sorts of projects, from socks to sweaters, to baby blankets and more. If you find your hands cramping from squeezing all these tiny needles, try some stretches to keep things loose.


Knitting Needle Sizes 3.75mm - 4.5mm

These needles match up with DK-weight yarn: it's just slightly lighter than worsted weight, making it super common for everything from sweaters to scarves to gloves.


Knitting Needle Sizes 4.5mm - 5.5mm

Arguably the most popular size of knitting needles, these workhorses are usually paired with worsted-weight yarn. This may even be the same yarn/needle combo you learned to knit with.


Knitting Needle Sizes 5.5mm - 8mm

The knitting needle sizes are growing larger, and as they do you'll notice that the knits work up faster and faster. Bulky or chunky-weight yarn is famous for being a quick knit. You can use practically any knitting needle type for this yarn, but keep in mind that if you're working with something large, those long circular needles will be a lifesaver for holding all the weight of the project. Fun fact: The sizes here start getting a little wonky.


Knitting Needle Sizes 8mm - 12mm

If you're in the "bigger is better camp",  let me introduce you to bulky yarns and their accompanying needles. You can experiment with textures such as cables that will really stand out when they're knit up in a super bulky fiber. 


Knitting Needle Sizes 12mm and greater

Make way for thick knits! Jumbo is the newest yarn weight category and uses the biggest knitting needles of all. You may need some serious guns to wield these hefty needles, so be on the lookout for plastic options: they weigh less.


Source : https://www.mybluprint.com/article/the-beginners-guide-to-knitting-needle-sizes