It's okay. store bought yarn will have oz/grams on it and your pattern may say use so many 50 gram balls of 'such & such' yarn
With homespun yarn, 50 grams of fiber spun into lace weight yarn will yield a lot more yardage than 50 grams of fiber spun into bulky weight yarn.
First thing to do is figure out which 'weight' of yarn you have spun. A standard yarn weight chart can be found here: http://www.yarnstandards.com/weight.html
Okay, so how do you know if the yarn you spun is fingering, DK or worsted (or any of the others?)???
You figure out your average Wraps Per Inch of your handspun http://www.fiber2yarn.com/info/wpigauge.htm
Put the two together and you should be able to figure out how much yarn you need to spin for a pattern!