Need ventilation advice

I have a 4X4X6.5 tent that I will be growing in but I need advice on the ventilation setup.
-What size exhaust fan and carbon filter do I need for this size tent?
-at what point should I start using the ventilation?
-any other advice would be great

a rule of thumb is 3x cubic ft. in cfm for the ACTUAL fan output. to get that, you have to deduct how much the filter reduces the airflow from the rated cfm to get the actual