Nicotine content varies from ejuice to juice. More conventional higher PG juices that include the tobacco ranges or the simpler flavour blends for beginner and intermediate electronic cigarettes tend to be in the following ranges:
0mg, 3mg, 6mg, 12mg, 18mg, 24mg.
10 to 12 mg is roughly the equivalent of one conventional strength cigarette.
Eliquids contain two main ingredients beyond diluted nicotine and flavourings; these are VG - Vegetable Glycerol, and PG - Propylene Glycol. PG and VG are commonly used as sweeteners and preservatives and are deemed safe and inert by USAs Food Drug Administration and the UKs FSA/Food Standards Agency.
PG creates throat hit, while VG enhances vapour (cloud) production. Higher VG juices are favoured by those with an allergy to PG or 'Cloudchasers'. Cloud chasing ejuices are more commonly stocked in lower nicotine concentrations, such as 0mg, 3mg, 6mg and some 12mg. VG is a thicker fluid and is unlikely to be well suited for clearomiser devices as they do not allow sufficient power and airflow to vaporise the VG based ejuice. VG juices work well with Subtanks, RDAs, Drippers etc.