I recently had an email from a spindler asking about wraps per inch (WPI) tables, as there are quite a few on-line, and they have different numbers! (A and B agree, then there are C and D and ... you can search google for "wraps per inch" to keep finding more!)
I posted "mine" here.
The scale I posted uses numbers from the CYCA, Craft Yarn Council of America. Though they don't include WPI on their scale.
And, oo-la-la, I see that CYCA has succumbed to pressure and now has a "0" for lace on their scale. I have been putting one in mine for a while :-)
The WPI's I use match those in the KnitPicks catalog and in their articles here, where they match up the CYCA scale to the WPI's. This also (I think) matches the card Nancy's Knit Knacks publishes with their WPI tool (the numbers are purposely blurred on their website).
I, too, was stymied at the diversity of WPI charts out there, but felt that using this one would give me the best match to commercial yarns -- a must for substituting in patterns more easily!
I find the numbers in the chart I use work well with the theory (from Mabel Ross) that if you fold your yarn in half and put it over the yarn gauge, the largest one that the folded-back yarn completely covers without any clearance will give you the needle size for a solid but well-draping knit fabric.
In fact, I use my knitting needle gauge sometimes to work out what my WPI is ... divide the needle's mm size in half, then divide that into 25.4 (mm/inch) to get the WPI of the yarn (VERY approximate since it's such a small sample!) So, if the 4 mm needle is the "winner", I have 2mm wide yarn, which would be 25.4 / 2 = ~ 12.7 wraps per inch, a DK weight yarn.
It gets worse if you try to find a YPP standard, but there are technical reasons why that's so impossible -- the ranges have to be wide, since density of the yarn is a huge factor in yards per pound. And then there's my current bugaboo -- I can't figure out if Alden Amos agrees with Mabel Ross in the balanced yarn theory -- that ply twist is 2/3 singles' twist or has his own, that ply twist is 1/2 singles' twist. I read that 10 times last night trying to figure out what he meant. Anne Fields quotes Mabel Ross, so she's taking her numbers as a given. And Peter Teal doesn't really discuss balanced yarn, since he wants to be aware of what the twist is in his singles, and he wants there to be a certain amount, so he discusses plying twist in those terms. Sigh. I'll dig Fannin off the shelf tonight and let him weigh in on the topic! (ETA: Fannin didn't quote numbers either, sigh... the mystery continues)
Oh, and one more thing ... As if to confuse the whole Bulky/Chunky issue, check out the CYCA table ... under 5 "Bulky" they list Chunky as another name for it; and under 6 "Super Bulky" They list "Bulky" as another name for that! So it's all very fuzzy at that end of the scale (ha-ha, literally!!)
Not to worry, plying posts are still in the works; I took photos of samples yesterday for "How to Ply a Thicker Yarn". Look for that post later this week.