In 2010 Mrj7j posted a helpful bit of info on nicotine levels in tobacco versus e-liquids, however, he made some mistakes and there's more to add to complete the picture.
( Mrj7j post ; Nicotine in E-liquid vs. Nicotine in Tobacco Cigarettes... Nicotine in E-liquid vs. Nicotine in Tobacco Cigarettes )
Most canadian KingSize cigarettes have 1 gm of tobacco. Most contain 1.6 to 3.6 milligrams total nicotine . There's about 20 drops of e-liquid per ml, and about 4-5 puffs/drop. At e-liquid of 16mg/ml, 1 drop is about .8mg total nicotine. (16 ÷ 20). 1 tobacco cig is about 8-10 puffs, and 1 drop of e-liquid is about 4-5 puffs, so 2 drops = 1 tobacco cig. As 1 drop = 0.8-1.8 mg total nicotine, 2 drops = 1.6-3.6 mg total nicotine. These amounts fairly compare with the 1.6 to 3.6 mg/gm/cig total nicotine in tobacco cigs.
However, total nicotine is not absorbed nicotine. No clinical studies which have measured absorbed nicotine in e-liquids, but tobacco tests estimate about 80% is absorbed.
In tobacco smoking, much of the total nicotine present in 1 cig is not inhaled as it burns out into the air and in the ashtray, and the last 1/2-3/5 " or so of the cig is disguarded. I estimate a cig with 2.4mg/gm of total nicotine content has only about 60% of it's tobacco actually use-inhaled, so 60% x 80% is about 48% (50%) absorbed nicotine, or 1.2mg/cig smoked.
E-liquid amounts absorbed can only be guessed at, though almost none is lost in holding and ashtray burning as with tobacco, although some amount is lost inside the atty's container and mouthpiece/cartridge polyfibre. ( provided you haven't de-bridged your atty )
Hope this helps....