For e-liquid, the typical nicotine recommendations are as follows:
1/2 pack per day or less = 6 mg nicotine
1 ppd = 12 mg
1 1/2 ppd = 18 mg
2 ppd = 24 mg
Figure on consuming at least 2 - 3 ml of liquid daily. Bottles are usually 10 or 30 ml volume.
PG and VG are often used together in different ratios in e-liquid. For example, a 50/50 PG/VG ratio. Many juice vendors offer a range of different ratios as far as PG/VG.
E-liquid generally has concentrated nicotine, propylene glycol (Pg), vegetable glycerin (Vg) and flavoring extracts.
The ratio of Pg to Vg is known as the pg/vg ratio, and a 50/50 blend is common.
PG = Propylene Glycol - the "flavor carrier" of e-liquid. A secondary source of "throat hit", but not as strong as the nicotine concentration. Some people have a sensitivity or even an allergy to PG. It's very thin in consistancy.
VG = Vegetable Glycerin - the "vapor maker" of e-liquid. Used as a sweeter in many food sources, and also as a skin emollient. It's very thick in consistancy.
How to Choose Between PG and VG