Depends on the cart and on whether you really mean cart or mean the screw on kind which are cartomizers aka cartos
cart holds about .4ml to .6ml
carto holds at least 1ml on decent size ecigs
You are not going to figure anything out. It depends on your
ecig, your mouth size, the size of your drags, how many drags you consider a cigarette to be. And most people don't vape that way. They usually vape more often than they smoked but for fewer drags.
After you get an ecig, use the same 5ml or 6ml bottle of
juice for several days and each day look to see how far the level dropped. Then you will know how much
juice you use in a day.