Casting on has is an art all it’s own. There are books dedicated to just this technique alone and depending on what you’re making/doing, you should know at least five at all times.
I dislike trying to use long-tail cast on for large projects (and I try to use other methods because this one is a little ugly for an edge). I know the whole trick about leaving a tail, wrapping the yarn, counting the wraps, then multiplying that length of yarn to the number I need. But you know what? It doesn’t always work. There, I wrote it! I find that method is a better measurement then eyeballing the amount of yarn you need, but I either end up with WAY too much yarn (usually the bigger the needs, the more yarn) or just missed the mark (converse issue of the former).
I figured out why this happens, it depends on how tightly you wind the yarn around the need and how tightly you actually make the cast on stitch. See how this doesn’t work out so well? Wind too tight, but cast on even a little loosely, there goes your measurement.
Also, don’t use the backwards loop cast on. Why? Because of the structure of the stitch when cast on (super stretchy), you end up with WAY too much yarn. This method is best for a handful of stitches, not for 100+.
I like to use the lace cast on method (and I stick to this one when I’m using smaller needles, but not necessarily lace. Like for a shawl, scarf, or cowl). Eunny Jang has an AWESOME page about this lace cast ons and I’m really linking it here for me to remember where the heck it is (oh, yeah, and you too. Sharing and all that).
But remember, when you have a project, look up a few cast on methods for the type of project you’re doing and chose accordingly. Not all projects need a long tail.
Working my crafty, old lady Friday night (Judge me, I dare you), -Stacy C