Not that simple. The flavoring counts towards the total content so if you want to
vape 12mg and add 20% flavor you've diluted your Nicotine by 2.4mg thus the finished mix is 9.6mg. You need to compensate the base nicotine by 2.4mg thus it needs to be 14.4mg when figuring in 20% of flavoring added. Now 20% is just a random total flavor example that I picked and flavor percentages vari from flavor to flavor and mix to mix
Here's some light reading for ya
Read my blogs before getting started
E-Cigarette Forum - dannyv45 - Blogs
then read hoosier's blogs.
E-Cigarette Forum - Hoosier - Blogs
then read the stickies at the top of the page.
this will explain a lot of the how's and why's.