Every new vaper knows the confusion. Shopping for your usual 12 mg/mL nicotine level, you don’t see the option there. Instead, the e-juice comes in either 0%, 0.3%, 0.6%, 1.2% and 1.8% nicotine. So what do you do? What’s the difference between nicotine strengths written as mg/mL and those written as percentages? How do you convert from one to the other?
Nicotine strength in mg/mL
Most of the time, e-liquid nicotine strengths are shown in mg/mL, which stands for milligrams per milliliter. This means that for every milliliter of e-liquid in the bottle, there is the specified amount of nicotine.
For a 6 mg/mL e-juice, this means every milliliter contains 6 mg of nicotine. If you need to work out the total amount of nicotine in a bottle or in a tank, just multiply the strength in mg/mL by the number of milliliters of it you have.
For example, if you fill up a 5 mL tank with 6 mg/mL e-liquid, you have 5 mL × 6 mg/mL = 30 mg of nicotine in your tank. In the same way, a 10 mL bottle of 6 mg/mL e-liquid contains 60 mg of nicotine in total.
Nicotine strengths as percentages
Nicotine strengths as percentages are very similar, but a little easier to understand. Instead of combining a mass (in mg) and a volume (in mL), percentages use the volumes of both. In simple terms, figures like 0.3% or 1.8% just tell you how much of the liquid in the bottle is nicotine.
This means that if you have some e-liquid containing 1.2% nicotine, any amount you measure out will be 1.2% nicotine and 98.8% PG, VG and flavorings.
Technically, this measurement is called “nicotine by volume,” in the same way the percentages on a bottle of liquor are “alcohol by volume” or ABV for short. “Nicotine by volume” is sometimes shortened to NBV too.
You could also work out the percentage by mass, if you wanted to, but e-liquid companies usually don’t do this. We work with e-juice in mL, so they do to.
Converting from mg/mL to percent and back
Converting from a nicotine strength in mg/mL to a percentage is really easy. Just divide the amount in mg/mL by 10. So if you have a 6 mg/mL e-juice, this is equal to a 0.6% e-juice. An 18 mg/mL e-juice is equal to a 1.8% e-juice. And if you had a high-strength nicotine base of 72 mg/mL, this would be 7.2%
The conversion couldn’t be any simpler. To convert back from percentages to mg/mL, just multiply it by 10.
More detail on combining weights and volumes
Practically, this is all you’ll need to know to switch between percentages and mg/mL values confidently. But if you’re interested in why exactly it works out like that, here’s a bit more information.
The issue is slightly complicated because values in mg/mL mix mass and volume. This convention originated in China, where the first e-cigarettes were made. It wouldn’t be a problem, but to work out a percentage, you need two volumes to use, not one volume and one mass.
To work it out for yourself, you need to know how much volume each mg of nicotine occupies in liquid form. Nicotine has a density of 1.01 grams per cubic centimeter, which means that 1,010 mg of pure nicotine takes up one milliliter. We can use this to convert mg of nicotine to mL of nicotine.
First, we need to find the total amount of nicotine we’re considering, in mg. As covered earlier, this just means multiplying the nicotine strength – say 6 mg/mL – by the size of the bottle – say 10 mL. So in this case we have 60 mg of nicotine. Using the density of nicotine, this works out to about 0.059 mL of pure nicotine.
So to work out the percentage, you divide the volume of the nicotine by the total volume of the e-liquid and then multiply the result by 100. This means that the 10 mL bottle of 6 mg/mL e-liquid has (0.59 mL / 10 mL ) × 100% = 0.59% nicotine. Since we don’t need to be this accurate, it would be listed on the bottle as 0.6%.
You won’t need to actually do this, but this explains why all you need to do to go from mg/mL to a percentage is divide by 10. Nicotine has a similar density to water, so it’s basically 1 g per mL, and this makes the math really easy.
Congratulations: You’ll never order the wrong e-juice again
If you aren’t too traumatized from the impromptu math, you can now confidently explain what mg/mL means, what the percentage values on e-liquids mean and convert between them easily. No matter where you’re ordering from, you’ll know exactly what you’re getting.