For me I just use a punch the buttons calculator, it is very simple.
First of all you want to determine how much of a finished product your going to make.
Let's say 30ml
In your case wanting 12mg/ml you need to punch some numbers.
30ml bottle x 12mg/ml = 360mg of nicotine.
360mg ÷ your 18mg/ml base = 20ml
So in a 30ml bottle add 20ml of your 18mg/ml nicotine solution. You have 10ml left to add flavorings or unflavored VG/PG.
If you were making a 15ml batch the math is the same.
15ml bottle x 12mg/ml = 180mg of nicotine.
180mg ÷ 18mg/ml = 10ml
So in the 15ml bottle you would add 10ml of the 18mg/ml base and have 5ml of room to add flavors or VG/PG.
For recipes that provide a percentage of flavor, say 5%, on the calculator it is 0.05 x (whatever bottle size you are using); 0.5% would be 0.005 and 10% is 0.10
With your 18mg/ml base, and making 12mg/ml juice, you have room for 33% other stuff. Very few if any recipes go beyond 20% flavoring and if they do you might want to look closer at them to see why.
Maurice
