I feel like such a dolt sometimes

Ok, so I've just started to sell my hand dyed recycled yarns and I've really been struggling to find the gauge of each yarn without knitting a test swatch. I've been working with large quantities of yarn which are all different thicknesses. There's just no way i can knit a swatch for all of them. I've heard the term "wraps per inch" before, but for some reason if just never tipped my radar. I need a new radar system apparently because WPI is a beautiful, more universal way to determine a yarn's thickness. I'm excited to measure all my newly dyed yarns when they dry!