I am planning on knitting a hat for a toddler using size US4 needles and 2 weight yarn. I am going to knit a swatch using the needles and yarn to determine how many stitches I need to cast on. I am planning on completing about an inch of 2x2 rib to start the hat and then knit in the round (making st st). Do I knit my swatch in the 2x2 rib in order to determine how many stitches I need to cast on? Or do I simply knit back and forth? Thank you for your help!
Toddler Hat
I’d do the swatch n stockinette stitch.
First, im going to tell you it is HIGHLY recomended that since you are going to be working in the round, you should do your swatch in the round as well…(smaller scale of course). Gauge can be sneeky and change when you knit in the round, from what you knitted flat…
Next Ill tell you to do your swatch in stockenette(Flat: knit one row, purl one row, In the round: Knit all rows)
All your pattern stitches, ribbing, ect…fall under that swatches gauge. 
This is how its done for all patterns, unless the pattern tells you otherwise…(theres always a “unless” isnt there?) If it says nothing about it, and just tells you gauge, do it in stockenette.
:knitting:
Melissa
Just knit a St st gauge for your hat. I like to use a needle one size smaller (or sometimes even 2 for the ribbing), but be sure to cast on very loosely. To insure a loose cast on I like to cast on on a bigger needle, or over 2 needles. I like ribbing to be nice and snug, but want the edge to stretch plenty.
As far as knitting your swatch in the round, that is often recommended and not a bad idea, but gauge can play funny tricks anyway. One way to do an “in the round” gauge swatch is to knit across and then, leaving a big loop and keeping the right side facing you all the time, go back and knit the row again. Keep doing that. Kind of like a giant i-cord. Add a few extra stitches because the edge stitches get loose doing this. I do this sometimes to determine “in the round” gauge, but then when I actually knit in the round my gauge may not match that anyway. So I have taken to not bothering (most of the time) to make an “in the round” gauge, I just work it back and forth. True it is sometimes a tad but I find it works for me.
I just read a thread on Ravelry about doing “in the round” gauge and some folks like to make a hat, or sleeve in the round to determine the gauge when doing an in the round sweater. It’s more accurate than a fake “in the round” gauge swatch. But what about when you want to make a hat to begin with? Ah, there’s the rub. 