Determining gauge in garter stitch

OK, this is such a dumb question. It’s been so long since I did a gauge swatch and since I knit with straight needles, I can’t remember any of this!

I have to knit a gauge swatch in garter stitch (which is knit every row, right?) so how do I count sts for a gauge? Do I count the knit row or the purl row? Any advice? This is for felted slippers so it’s not a big deal but I’m substituting yarn and I want to get it close.

Thanks for the help!

It’s easier to see the purl bumps, so I usually count them.

I actually thought, what the heck, let’s just see what happens so I did a swatch. I’m glad you confirmed what I did, it was easier to see the pearl bumps so I counted them. I’m WAY off on gauge but it looks like everyone else on Ravelry was too with this pattern and yarn combo so I’m going to use the bigger size.

Thanks so much!!