So many factors come into play.
What are you vaping it with? An atty that runs really cool and doesn't have alot of surface to liquid area with the coils will go through it slower than a really hot atty with several winds and really thick wire in the coils. Dualies cranked up to prime performance will drink it by the ml instead of by the drop. Direct dripping vs using a cart, tank, or carto also has a significant impact on how much liquid one goes through and how quickly.
The PG/VG ratio also can effect it some. For me, it seems higher VG liquids go a little faster.
Nic level can make a big difference as well for alot of people. Someone using a 24mg nic liquid might not feel inclined to hit it as often as someone using 4mg. Of course this varies widely from person to person....it's not all about nic to everyone.
For me...the most I've ever used in one day was 4ml @ 4mg nic. I was sucking on a CE2 type carto all day and never put it down. Had I used higher nic levels, it probably would have made me ill! I doubt I would have hit it nearly as often with higher nic levels.
So it's just plain hard to say. For me it's 2 to 4 ml a day. If I'm in a situation where I can enjoy the PV at any time I wish, I use lower nic, and vape like a research monkey (from 3ml to 5ml [with dualies I could easily go up to 5ml] depending on atty/carto type). If I'm working alot, and can only vape during breaks and such...I way UP the nicotine and hit it more like real cigs. On days like that...2ml is usually more than enough for me.
In short...get more than you think you'll need once you find some flavors you like. Take advantage of bulk prices on your 'go-to' liquids. Keep a variety of nic levels to suit your moods and needs. It won't take long to find ways to do it all for just a few cents a day if budgeting is a concern.
