Swatch take two! Same stitch as the one the other day, just a different yarn (I’m quite set on the stitch I want to use, I’m just looking for yarn that will give me the fabric/sizing options I want).
This one is Berroco’s Mochi in Plum, and it’s a beautiful example of why I will never ever EVER be able to tell you what needle size to use.
I’m swatching on a US 3 (3.25 mm) and getting a smidge under 4 stitches per inch. If I wanted firmer fabric (closer to 4 stitches per inch), I’d need to use a US 2 (2.75mm), maybe even something smaller. The yarn band recommends you use a US 9 (5.5mm) to get 4 stitches per inch.
Read that again.
To get 4 stitches per inch, the ball band recommends you use a US 9 (5.5 mm). To get 4 stitches per inch, I need to use a US 2 (2.75 mm).
There’s a decent chance there’s a knitter out there who would need to use needles bigger than what it says on the ball band to get that gauge (just like I need to use smaller needles).
With that sort of range, a needle size recommendation can never be anything more than a guess. The only way to figure out which needle size you’ll need is to swatch.
The more you knit, the more you’ll learn what you’ll probably need which helps you know where to start (I know I can usually knit most worsted/aran stuff on 3s, most sport/dk stuff on 1s or 2s, and most fingering on 0s). But I still have to swatch to be sure.
And I can tell you ‘check the ball band to see what it recommends and start there’ or, if you really push I can tell you ‘eh, I usually use 0s for skinny yarn and 3s for fat yarn.’ But that’s pretty meaningless when there’s that much potential range.
The real answer is that you have to put in the time experimenting to learn what works best for you. Nothing I can tell you is ever going to come close to learning what works for you.
And sure, if you TRULY do not care what size the finished thing comes out or what the fabric feels like (or if you don’t mind ripping it out if you don’t like how it comes out), you can take that risk and just knit it. It doesn’t do me any harm. But if you want it to be a particular size, swatching is the way to do that.