this is an interesting question. there is no one size fits all answer because everyone has a unique sensitivity to the aromatase enzyme. dose will depend on A, your level of sensitivity, B, the dose and type of gear used, and C, what your goal is. 

you want to control estrogen much closer when cutting than you do bulking. although too little estrogen will cause issues like dry, painful joints and although estrogen resensitizes the androgen receptor, too much estrogen will make it harder to lose fat and will make you hold more fluid on a cut. so a little more AI is going to be ideal for cutting. when bulking a little less AI will allow you to hold more fluid and you can use that weight to push more lbs in the gym. 

so there is no exact science. it will take listening to your body and figuring out what you need. a jump off point for adex might look like .5mg EOD, assuming you're using a gram or less of test. from there, you can lower it if needed. you may go as low at .5mg 2x wk when bulking. even .25mg 3x a wk on lower doses of gear. i wouldnt go much lower than that.  

keep in mind that if you kick start a cycle with a compound with high conversion, like dbol, slightly more may be required during that part of the cycle.