You can use a fancy wraps-per-inch device, but I went ahead and wrapped my yarn onto an embroidery floss holder. These just happen to be one inch wide and are great for those who like to do sampling and keep track of what they do. It's even better for absent minded people who tend to misplace their expensive fancy wood one. The floss cards come in packs of 100 and are inexpensive, so when I lose one, I can just go get another.
Determining wraps per inch can be tricky and you may want to do it more than once for any given bit of yarn. It requires wrapping the yarn on evenly, so the strands are next to each other in a natural way. A good thing about using the floss card is the little edges keep you from "cheating" and going over a marked line. You can still cheat as I did below by cramming the threads in to make sure it is 14 wraps per inch for anyone who may be counting. That's why it is good to do the check more than once and with different parts of your yarn. Spinning is a manual, and therefore, uneven process. In my mind, it is the random imperfections that make handspun so beautiful and fun to knit.
Knowing wraps per inch is a boon to the hand spinner, because you can find out how thick the yarn is for any given pattern by looking it up on Ravelry. This is also one of the reasons I love Ravelry. I used to have to divine yarn thickness based on knitting gauge, needle size and tiny pictures of the yarn in magazine. Now, I can just click onto Raverly and get the wpi for any yarn for most every pattern. With some swatching and experimentation, I can find the yarn I want. This is how I am able to spin this yarn for an Alice Starmore Kinsale.
You can find this gadget at many stores and online spinning gadget providers. Here it is at The Woolery--you'll find it if you scroll down the page http://www.woolery.com/Pages/spinaccess.html. You can find it at Woodland Woolworks at http://www.woolworks.com/Shop/Spinning/Spinning-Aids.1/Spinners-Control-Card. You might also be able to find it at the next fiber festival you attend or at your local spinning store, if you have one.
Thank you for visiting my blog. Please stop by again. You can find this and other spinning and fiber related tips on my website www.whorlwindweaver.com.