Sizing needles

I received a bunch of knitting needles that belonged to my grandma. The problem is, I have no clue what size they are. I don’t have a gauge ruler (or whatever they’re called). Is there another way to determine what size they are, for instance, making a gauge swatch?

That’s not a really reliable way to size them. It would be best to get a knitting gauge, they’re only a couple dollars wherever they sell needles, even at Walmart.