Calculating... I think I've used in the last month a bit less than 30 ml of 18mg e-liquid, plus about 30 ml of no nic VG liquid made by myself...
So, it makes about 1ml of 18mg and 1ml no nic a day, plus maybe 1/2 prefilled cart. Although I still smoke some analogs (maybe 0-5 a day). Coming from 40 analogs a day, I think it's a good change. I think I'm using less nicontine, although it's only "average", some days I've smoked 20 analogs and vaped a lot too (days with too much work...

).
I think I could use even less nic if I could do an e-liquid with a good throat hit by myself... but my no nic liquid has no hit at all (lots of vapor to play with, but nothing else), and that makes me use more nic liquid when I'm nervous... or go back to analogs

).