Effect of Changing a Needle Size

Is there a table that gives an approximation of the effect of moving up or down one needle size? For example, what percentage smaller would something be if knit with a size 7 in stockinet instead of a size 8 in stockinet with the same yarn?

I’ve started knitting a cowl with size 8 circular. The pattern doesn’t have a gauge (probably since it doesn’t matter much for a cowl). I think I’d prefer a tighter weave and would start over with a 7 if it only made the cowl 5-10% narrower. If it made it 25% narrower I’d just stay the course out of fear a smaller cowl wouldn’t fit over by big head.

Sure I could make a couple swatches but having a table created by a knitting math wizard would be sooooo handy!

I’ve never seen anything like what you describe. Mostly, because each person’s gauge is so different. My knitting with size 7 needles would probably be VERY different than yours (and everyone else’s). So your best bet would be to make a gauge swatch with the different needle sizes and see how they both turn out.

IMHO, I don’t think there will be much difference between size 7 & 8. Switching 2 or 3 sizes would change things a LOT.


Swatching is best. FWIW when I do rib I’ll go down 2 or even 3 needle sizes OR I will decrease out about 10% of the stitches, say from 40 to 36 rounded to the nearest number that gives me the multiple I need. If I go down 3 sizes I’ll most likely round up, 2 needle sizes then I’ll round down. I don’t know if that’s info that you can use or not. I think I’d do at least a half hearted attempt at swatching and decide which needle size made the fabric I like best before starting the cowl. Based on that I’d decide if I needed to add stitches or start with fewer. Then I’d probably frog and use a different size. I get a lot of knitting mileage out of my yarns.

What cowl pattern are you using? Can you link to it please?

It’s for an intro to stranded knitting class. We’ve been asked to do 10 rows of 2x2 on #8 before class. At class we’ll learn a 12-st repeat chevron pattern & alternate colors each row. The instructor used worsted Malabrigo. I’m using worsted Berroco Fuji that seems finer so I added another 12 st. The rib is kind of loose. Based on your reply, maybe I should do the rib on #7 and decide about whether to stay on 7 or switch to 8 at the class? Would hate to burn class time with frogging!

The math part of my original question is based on this:
– a #7 is 4.5mm and a #8 is 5mm.
In other words, a #7 is 90% of the size of a #8. Does that mean that using a #7 instead of a #8, will make something that is 90% as big?

Math is wiley thing!

As this is a class project I would say, do what you’re told in class. I thought you were just working out what to do with a pattern you like.

Math and I generally keep a respectful distance from each other. We just don’t get along, I’ll leave the real math for someone else to comment on.

It’s unfortunately not as simple as that. Be awesome if it were. I’ve done swatches in close sizes like that and not had a significant difference in gauge. That said, you’d still need to calculate gauge on a swatch to have something to do the math against.

Checking out the yarns, your substitution is definitely much lighter than the one the teacher is using. Even using the same size needle, you might not get the called for gauge of the cowl. (And I don’t see how gauge can’t be important if you’re working this thing bottom up like it sounds like. You can end up with something quite a different length!) Not to mention the difference in fibers is going to throw other things off as well.

Ordinarily, since you’re making an actual object you’d probably like to wear instead of just a test piece, I’d say use what gives you the fabric you like, then do the math to calculate how many more stitches you need to cast on to get the right size. But if this project is to be stranded, there could be pattern repeat issues.

Do you have the option to discuss this with the teacher in advance? She’s obviously trying to keep it simple for everyone, but even if you were all using the exact same needles and yarn, everyone’s gauge would be different.