Measurement of hand-spun yarn is rather... hit or miss. Accuracy can vary quite a lot, and then it can vary quite a lot again, when it hits water. (It his highly advisable to skein your new yarn, wash, and dry it, before trying to use it for knitting/crochet/weaving/macrame/tatting/rigging sailing ships. Sets the twist [like setting a curl in your hair] and makes it easier to work with.)
There are two ways to measure. One that is PROBABLY, under ideal conditions, most accurate, is by weight. You need a really accurate scale:
This one is from Harbor Freight, and weighs in tenths of a gram. I think I got it on sale for $14. I know it was under twenty. You get a yard of your yarn, weigh it, weigh the rest of the skein, and do the math. If you stick with metric, the math is even easy. Drawbacks are, for real accuracy, you need to cut the yard from the rest of the skein, if you've spun frog hair (finer than frog hair? that saying?) you may need to weigh five or more yards to get it to freaking register as weight, and if you spin unevenly, the whole thing's out the window.
The more traditional method is to wrap the yarn around something of known circumference, count as you go, and do that math. (This is where the song "Pop Goes the Weasel" is from. Around and around the swift, and old production ones would make a pop or click every one, five, or ten yards. Which is cool, except this song is guaranteed to piss me off thanks to my friend W, who introduced me to Plants Vs. Zombies. BUT I DIGRESS.) For winding off, I use a 1.5 yard niddy-noddy:
(Fun story, since I'm digressing all the hell over the place anyway: I used to hang out with a former pro hokey player, and when he'd jokingly threaten about hockey sticks, I'd tell him I was ready to take him down with my niddy-noddy. After a couple years, he finally saw a picture of one and was all "THOSE THINGS LOOK DEADLY!" and I was "Well, duh, I'm not gonna threaten an intruder with a pillow for fuck's sake.") Anyway. My usual method is to count as I wrap, unless the hub, kid, and cat are anywhere near me, then I lose count, yell at everybody, and go back and count later. Depending on how much it shrinks in the wash, I will multiply by 1.25 instead of 1.5. Drawbacks include all the above, plus for true devotees of accuracy, the way the wrap gets larger/longer as you go on really big spins will make you kinda crazy. But it's a good way to get a ballpark when you can't even guess to within a hundred yards because you had a migraine while you spun it. I know I chronically underestimate this way, but I've never run out of yarn and haven't ever heard from anyone else who bought my yarn that it was underestimated. This is the method I use most often, and is used most by spinners, at least the ones I hang out with.
Since I was taking pictures anyway, and this was on the niddy-noddy, I got a closeup:
It's a four-strand hawser ply. It's how they used to make rope. Z-twist four singles, then do two pairs of them, Z-twisting AGAIN, then S-ply the whole shooting match. For as much twist as there is in this stuff, it is awfully not-squishy. When I finished it, my thought process went "awfully sturdy... feels like rope... no shit Julie, you think?" But there are spinners who swear by this for cuffs and socks. Dunno, I think I'll be sticking cable ply if I want to knit or weave body armor.