An estamate would be 6mg to 12mg of nic contained in each cigerette, depending on the brand of cigerette you are smoking. One does not absorb all the nicotine contained in the tobacco, and how much you absorb depends on several factors. Rough absorbtion estamates would be 10% to 20%, and based on 8mg analogs you would be delivering 16 to 32 mg per day from your one pack a day analogs.
I have not been able to find any verifiable data with regard to nicotine absorbtion from vapor. "Assuming" it is roughly the same as analogs at 10%-20%, if you vape 4 ml of 18mg liquid per day, you would be getting 7-14 mg of nicotine from that level of vaping.
When I do the math it always seems to indicate one would need to vape 5ml or more of high strengh nic juice to replace the nic delivered in a 1-2 pack a day habit of analogs, and yet as Firehorse points out it seems to be differant for everyone. I vape 0mg to11mg when i just feel like vaping, but when i feel the "need" for a analog, I vape 18 and it works for me. You can divide up that first bottle and make a few differant strengths with the PG/VG.
Happy vaping and good luck.