Are you asking how many classes you should take when you attend a UC? 12 credits is full time, but you normally want to take 15 credits to graduate on time. So it really depends on the units for each of the courses. At UCSC, almost all of the courses here are 5 credits each (not including lab). So students normally take 3 classes minimum, but you'll see students taking more or less (I'm taking 22 units).