When I first got my Dripbox 160, I went through almost 30 ml with it the first day. I've since slowed down a bit and went back to my previous usage level, so now on various drippers and RTA's I'm going through about 20-25 ml a day.
The funny thing when I first started vaping, I was using 3 ml a day and I thought I was vaping a lot. Although if you look at the numbers, I'm getting about the same amount of nicotine. When I started vaping, I was vaping 24 mg juice and now I'm vaping 3 mg juice.