You need an eLiquid calculator. I've been using one called EzMix lately. I have also used eJuiceMeUp. Google will find several others.
They all work about the same. You input how much eLiquid you want to make (5ml, 10ml, 30ml, etc.), what PG/VG ratio you want to end up with (50/50, 60/40, 65/35, etc.), and what you want your final nicotine strength to be (4mg, 6mg, 12mg, etc.). Then, you input the name of the flavor(s), and how much of the total mix you want it (each) to be. For example, if you were making a bottle of grape flavored eLiquid, it might take 5% grape flavoring to produce the taste you are looking for based on the flavoring concentrate that you use. When you input 5% grape, the calculator will tell you how many milliliters of flavoring to add to get there. If you are making a 10ml bottle of juice, you would add .5ml of flavor, if you are making 30ml of juice, it will have you add 1.5ml of flavor. If there is more than one flavor in your mix, it will tell you how much of each to add based on the percentages that you input for each.
Here is what a 3 ingredient recipe looks like in Ez-Mix
