Best way to find this out for yourself is experimenting with slowly titrating the dose up. Some guys only need 500, 750, 1000 per week, others use up to 2000ius/wk. This somewhat correlates to your weekly total of mg's of gear being used. But again, best if you find out for yourself instead of just having someone tell you "What you should be using". As a guide most start out with 1000iu per week. I've been using 1000iu/wk with runs for years now and I always feel good, I've never felt like I needed to go above 1000iu/wk.
Through understanding side effects, a lot of guys instinctually can feel when they need to lower or raise ancillaries like AI's or HCG by how they feel and how they look in the mirror, ie: water retention. But the best way is by being able to read blood panels and by comparing multiple blood panels which requires getting your bloodwork done on a regular basis and knowing how to read the panel. It's very easy to learn how to read blood panels, it just takes a little time to study and read into it, well worth the invested time.