One cartomizer will hold approx 1ml on it's initial filling. The XL sized cartomizers should hold about 1.5ml.
You don't want to refill the cartomizer in the traditional sense. You want to top it off as it uses
juice. How often you top off will depend on your
vaping pace. Look for the vapor to start thinning out. If you wait, it will start tasting burned. If you wait too long, you can burn the filler in the carto and ruin it. So, top off as frequently as you can. Just drip some
juice in it and let it absorb until it looks slushy on top. If you overfill it, just take it off and blow out the excess. After some practice, you'll know how often and how much to top off.
Comparing a carto to a certain number of cigarettes is largely an exercise in futility. It would depend on what kind of cigs you smoked, the nic content of the juice, your technique, your absorption rate and a bunch of other things. It might make more sense to try to predict how much juice you'll vape in a day. Most average vapers go through about 3-5ml/day. That's according to polls done around here and seems correspond with most of the individual posts I've read. Again, how often you top off your cartomizer will depend on your own consumption, but do it as often as possible. It helps to have a drip tip so that you don't have to pry off the little rubber cap every time. That'll make it more convenient and promote frequent topping off.
