Here is a list of common nicotine strengths in retail e-liquid, along with a nameset that covers the whole range (the description 'high' for example can be given to anything from 16mg to 36mg, it just depends on how many steps that vendor has in their range and is basically meaningless).
Also see the notes, as they are relevant.
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strength in mg/ml | strength as percentage | name / notes
__________________________________________________
0mg.......... 0%.......... zero nicotine [1]
3mg.......... 0.3%....... super-low [good for high-power rba use]
6mg.......... 0.6%....... low [good for high-power rba use]
12mg........ 1.2%....... medium-low
(16mg)...... 1.6%....... medium-minus [not a common strength at retail]
18mg........ 1.8%....... medium
24mg........ 2.4%....... medium-high
(30mg)...... 3%......... medium-high plus [not a common strength at retail]
36mg........ 3.6%....... high
45mg........ 4.5%....... super-high [good for low-efficiency minis used by beginners]
__________________________________________________
--all stronger solutions are for dilution before use--
-----------------------
Notes
1. Note that if a NET has been used for tobacco flavoring (a natural tobacco-extracted flavoring), then it is often possible that there is some nicotine present in very low strength (perhaps 0.1% or so). Therefore, if you absolutely wish to avoid inhaling any nicotine, then a tobacco flavour may be wise to avoid.
However you might also note, of course, that inhaling any nicotine at this microscopic strength is probably going to deliver less to the body than that delivered daily by consumption of a proper diet (as vegetables contain nicotine and the resulting nutrient delivery can be measured in the blood - everyone tests positive for nicotine, for this reason).
2. People have a widely-varying tolerance to nicotine, caused by genetic differences. It is absolutely beyond doubt that this is genetic and has nothing to do with smoking or built-up tolerance, although recent smokers will show a tolerance effect that reduces over time. Some people (eventually, after the smoking-induced tolerance effects have worn off) can vape no higher than 6mg strength; less commonly, some need 60mg strength to avoid relapse to smoking. The bulk of users fall around the 18mg mark eventually, after the history of smoking recedes in time. After a plateau at that point (and this is a plateau measured in the gradual reduction of nicotine strength commonly experienced by vapers who have ceased to smoke), the strength can often be reduced further, gradually, over time. We know this from the reports in the millions of posts on ECF, which is in effect the world's largest smoking cessation resource.
(Please note that this representation is consistent with delivery in average-efficiency hardware such as a tankomiser on a 900mAh battery device, and is not accurate with low efficiency products such as minis, which tend to require a significant increase in nic strength to work at all; or with high-efficiency hardware such as some RBAs, which require a reduction in all factors in order to avoid overload.)
This shows a number of things:
i) Nicotine itself does not create tolerance
ii) Smoking creates tolerance
iii) Normalised* levels of tolerance to nicotine vary considerably, and are genetic in nature
iv) There is a factor 10 difference across the range, represented on a graph by a typical bell curve line from 6mg to 60mg, with the bulk around 18mg, and slightly more at the low end compared to the high end.
* meaning after smoking cessation and after a suitable timelapse to allow the effects of smoking to recede (or without previous smoking)
3. The names for the strengths are basically meaningless as everyone has a different idea of what any name might mean, and a vendor's range is generally named according to how many steps they have in their range. As a result "high" can mean just about anything, even 16mg - which is not even medium strength when taken as part of a full range.
4. The highest retail strength (refills sold as suitable for vaping, out of the bottle) is 45mg. It is mostly used in mini ecigs that (a) have poor efficiency, and (b) are in use by beginners with poor technique. For any other application it would be too strong most of the time. It does work, though, for people with ultra high nicotine tolerance using atomizers with a low conversion efficiency. (On average only 50% of the nicotine in refill liquid is transferred into the vapour, measured in minis using cartos and some clearos on mid-size units; also some early RBA types. Beginners may get much less, perhaps as little as 10% of the marked strength, due to suboptimal technique.)
45mg was introduced after several published and unpublished clinical trials of vapers (such as Eissenberg 1, Bullen et al, 2010) reported that regular strengths of refill liquid delivered no measurable nicotine in the vapers tested (or very little). There was little or no visible increase in plasma measurements above the baseline present from the diet. These tests had numerous issues that meant the results were not universally applicable, but nevertheless it indicated there was a problem. Unmentored beginners using mini ecigs were tested - and it is obvious to any vaper what the problems are with that arrangement: poor hardware efficiency together with poor vaping technique. Therefore a high strength refill was introduced first by Intellicig, then NJoy, to counter this problem: it meant that a beginner with entry-level gear could receive some nicotine from use - otherwise the device is basically just a placebo.
45mg used by experienced vapers in high-efficiency hardware will have too strong an effect except for those at the highest level of genetic predisposition to high nicotine tolerance (some people can consume what appears to be inadvisably large amounts with no noticeable effect, and lower strengths are ineffective for them). Normal people will stop after a few seconds and realise that some sort of downward adjustment is needed.
5. RBAs can deliver a massive amount of vapour, therefore all components in the refill are delivered at multiples of the level received from a clearo or even a tankomiser. It used to be rare to find a vaper consuming as much as 10ml a day with pre-RBA gear, as high-volume chain vaping like this is about equivalent to 60 a day smoking or thereabouts; but now some RBA users vape up to 20ml of refill a day, it's like pouring it down the sink. As a result, RBA users commonly reduce the nicotine level to 6mg or even 3mg in order to avoid over-consumption. In an RBA this is about equivalent to 18mg in a tankomiser or 24mg in a carto or clearo that isn't too efficient.
6. DIY mixing is best done with 54mg, 60mg or 100mg base. For some applications 200mg can be used. In general there is no need for any stronger base, as further savings are not significant, plus the fact pure nic should only be handled in a lab since a fume cupboard is needed.
-------------------------------------------
Also see the notes, as they are relevant.
__________________________________________________
strength in mg/ml | strength as percentage | name / notes
__________________________________________________
0mg.......... 0%.......... zero nicotine [1]
3mg.......... 0.3%....... super-low [good for high-power rba use]
6mg.......... 0.6%....... low [good for high-power rba use]
12mg........ 1.2%....... medium-low
(16mg)...... 1.6%....... medium-minus [not a common strength at retail]
18mg........ 1.8%....... medium
24mg........ 2.4%....... medium-high
(30mg)...... 3%......... medium-high plus [not a common strength at retail]
36mg........ 3.6%....... high
45mg........ 4.5%....... super-high [good for low-efficiency minis used by beginners]
__________________________________________________
--all stronger solutions are for dilution before use--
-----------------------
Notes
1. Note that if a NET has been used for tobacco flavoring (a natural tobacco-extracted flavoring), then it is often possible that there is some nicotine present in very low strength (perhaps 0.1% or so). Therefore, if you absolutely wish to avoid inhaling any nicotine, then a tobacco flavour may be wise to avoid.
However you might also note, of course, that inhaling any nicotine at this microscopic strength is probably going to deliver less to the body than that delivered daily by consumption of a proper diet (as vegetables contain nicotine and the resulting nutrient delivery can be measured in the blood - everyone tests positive for nicotine, for this reason).
2. People have a widely-varying tolerance to nicotine, caused by genetic differences. It is absolutely beyond doubt that this is genetic and has nothing to do with smoking or built-up tolerance, although recent smokers will show a tolerance effect that reduces over time. Some people (eventually, after the smoking-induced tolerance effects have worn off) can vape no higher than 6mg strength; less commonly, some need 60mg strength to avoid relapse to smoking. The bulk of users fall around the 18mg mark eventually, after the history of smoking recedes in time. After a plateau at that point (and this is a plateau measured in the gradual reduction of nicotine strength commonly experienced by vapers who have ceased to smoke), the strength can often be reduced further, gradually, over time. We know this from the reports in the millions of posts on ECF, which is in effect the world's largest smoking cessation resource.
(Please note that this representation is consistent with delivery in average-efficiency hardware such as a tankomiser on a 900mAh battery device, and is not accurate with low efficiency products such as minis, which tend to require a significant increase in nic strength to work at all; or with high-efficiency hardware such as some RBAs, which require a reduction in all factors in order to avoid overload.)
This shows a number of things:
i) Nicotine itself does not create tolerance
ii) Smoking creates tolerance
iii) Normalised* levels of tolerance to nicotine vary considerably, and are genetic in nature
iv) There is a factor 10 difference across the range, represented on a graph by a typical bell curve line from 6mg to 60mg, with the bulk around 18mg, and slightly more at the low end compared to the high end.
* meaning after smoking cessation and after a suitable timelapse to allow the effects of smoking to recede (or without previous smoking)
3. The names for the strengths are basically meaningless as everyone has a different idea of what any name might mean, and a vendor's range is generally named according to how many steps they have in their range. As a result "high" can mean just about anything, even 16mg - which is not even medium strength when taken as part of a full range.
4. The highest retail strength (refills sold as suitable for vaping, out of the bottle) is 45mg. It is mostly used in mini ecigs that (a) have poor efficiency, and (b) are in use by beginners with poor technique. For any other application it would be too strong most of the time. It does work, though, for people with ultra high nicotine tolerance using atomizers with a low conversion efficiency. (On average only 50% of the nicotine in refill liquid is transferred into the vapour, measured in minis using cartos and some clearos on mid-size units; also some early RBA types. Beginners may get much less, perhaps as little as 10% of the marked strength, due to suboptimal technique.)
45mg was introduced after several published and unpublished clinical trials of vapers (such as Eissenberg 1, Bullen et al, 2010) reported that regular strengths of refill liquid delivered no measurable nicotine in the vapers tested (or very little). There was little or no visible increase in plasma measurements above the baseline present from the diet. These tests had numerous issues that meant the results were not universally applicable, but nevertheless it indicated there was a problem. Unmentored beginners using mini ecigs were tested - and it is obvious to any vaper what the problems are with that arrangement: poor hardware efficiency together with poor vaping technique. Therefore a high strength refill was introduced first by Intellicig, then NJoy, to counter this problem: it meant that a beginner with entry-level gear could receive some nicotine from use - otherwise the device is basically just a placebo.
45mg used by experienced vapers in high-efficiency hardware will have too strong an effect except for those at the highest level of genetic predisposition to high nicotine tolerance (some people can consume what appears to be inadvisably large amounts with no noticeable effect, and lower strengths are ineffective for them). Normal people will stop after a few seconds and realise that some sort of downward adjustment is needed.
5. RBAs can deliver a massive amount of vapour, therefore all components in the refill are delivered at multiples of the level received from a clearo or even a tankomiser. It used to be rare to find a vaper consuming as much as 10ml a day with pre-RBA gear, as high-volume chain vaping like this is about equivalent to 60 a day smoking or thereabouts; but now some RBA users vape up to 20ml of refill a day, it's like pouring it down the sink. As a result, RBA users commonly reduce the nicotine level to 6mg or even 3mg in order to avoid over-consumption. In an RBA this is about equivalent to 18mg in a tankomiser or 24mg in a carto or clearo that isn't too efficient.
6. DIY mixing is best done with 54mg, 60mg or 100mg base. For some applications 200mg can be used. In general there is no need for any stronger base, as further savings are not significant, plus the fact pure nic should only be handled in a lab since a fume cupboard is needed.
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