I took 20 units this semester. That’s 5 classes total. The minimum amount of units I have to take in L&S is 13. Most students take 16 units. That’s 4 classes.
Before I get into my experiences, I should explain what units mean exactly. The number of units a class is assigned is based off of hours of work needed to put into each class outside of the predetermined lecture and section time. The reason students usually stick to around 16 is because more than that tends to start to be overwhelming and very time consuming, as I now know first hand.