It may seem like a really simple question from the title but it's a little more complex than that. I'm going to be refilling my cartomizers with my own e-juice. I want to get the most bang for my buck - highest nicotine content per dollar and cut it down. I'm confused if it is xx mg of nicotine per vial/bottle (ie., mg=total mg of nicotine in bottle) or xx mg of nicotine per ml in the vial/bottle (ie., mg*ml=total mg of nicotine in bottle). Is there a standard, or a way to tell? I haven't seen it mentioned on any of the sites I've come across and I think it's definitely important to know when mixing something as potentially toxic as nicotine.