Unidentified Yarn Size or Weight

I have a very difficult time deciding whether some yarn is fingering/fine/baby or whether it is sport/baby-sport.

It's okay when I still have the wrappers on the skeins, but with those without wrappers, it's hard.

I finally took my G hook and some of each of the yarns which still had labels. I made a small square, some dc's (double crochet stitches), and three rows. And then I made a note I will keep, noting the gauge for each size yarn.

Now, all I need to do with any UIY (unidentified yarn) is to make a quick square for gauge and then tape or pin a scrap of paper to it for the future if I cannot use it in the project I am working at that moment.