Some folks say that cartridge or cartomizer is the equivalent of 1 pack of cigarettes. But, there are so many variations available you can't really make a blanket statement. However, in my personal opinion, a KR808D-1 cartomizer is the equivalent of 1/2 pack of cigarettes.
Since the KR808D-1's are designed to be disposable, you can refill them but the atomizer degrades after several refills, and you tend to use them up faster. Or draw on them harder to get the same vapor hit as when the cartomizer was fresh.
I saw a peer reviewed study recently (I'll have to find it again) that tried to measure the amount of nicotine an e-cig delivers. As I recall, it was less than the advertised strength. So this could explain why you appear to be vaping more than you used to smoke.
If anyone is interested, I can try to locate the study.