I've mentioned it before, but it bears repeating: when you're buying yarn, the only measure that really matters is yardage.
Oh, you'll see patterns that call for, say, six or eight or twelve or eighteen ounces of a name brand, never specifying yardage. I suspect that such a yarn company, who paid the designer for developing the pattern, is hoping you won't feel secure substituting another yarn. And without the ounce-to-yard equivalent, it would be a little dicey, for you'd have to deliberately overbuy to have enough.
But look at any pattern on Ravelry (dot com) and you'll see the buying instructions expressed in yards. As they should be.
Have you ever wished you could buy just that certain number of yards of yarn? "Just wind me off 178 yards of that gorgeous angora, please."
Nope. It's the whole skein or nothing.
Not so with roving, the raw stuff from which your yarn is hand spun. Though some fiber does come prepackaged by the ounce or two (the pygora clouds I bought from Applebright Farms were put up that way, of necessity, being wound in brown paper like a jelly roll), in many cases you can ask for . . . oh, about five and a half ounces, to take a not-round number . . . and the proprietor will dutifully wind you off a good guess, weighing it in a preweighed bin until the right amount has been added. Like hamburger from a butcher shop. Or half a pound of nails from the hardware.
Then it's up to the spinner to make it go the distance.