6-10ml per day, depending on if I'm working or not. Always 6mg nicotine though, that doesn't change for me. Lately most of my vaping has been done with a dripper between 40-55 watts.
Edit: I think type of device used should be considered, or at least the power you're normally vaping at as that will consume more/less juice per hit depending on the mod/atty/juice/etc.