What dimentions should a quilt be to fit a queen or king sized bed?

I plan on making a my very first quilt. I plan on using 6x6 squares and tying it with yarn. However I'm not sure how large I should make it. I'm still in college but want this to be something that I can keep for a long time. Since I'm not sure what size bed I will have in the future (king or queen) I'm not sure what size to make the quilt so that it will fit both beds well. I want it to have more than enough overhang so we can tuck it under the mattress easily. Any suggestions would be appreciated.