It depends on what trainning program im following right now im doing 4 exercises for 17 sets low volume,in contest prep or high intensity training ill do 12 sets!
I have a different approach than most for determining the number of sets I use for any body part. I go by the pump I am feeling. If you pay attention to your pump, you will notice that when you start feeling one, it will make the trained body part feel tight and hard. At some point after a certain number of sets your worked body part pump will go from feeling tight and hard to feeling kind of jellyish. I stop working the body part when my pump feels jellyish. I note this in my training log, then stop working that body part.
Different techniques change the onset of this jellyish feeling. Usually with chest it takes a lot of sets compared to other body parts, but I can get there faster if I use forced reps or negatives.
I train most body parts once sometimes twice a week. I tend to randomize the days I work out during the week to avoid adaptation. I go by feel. If I feel tired or lack motivation, I usually take the day off and work those body parts in the split another day.