Umm, 12% is 120mg per ml. Even diluted with 20% flavoring that's still highly concentrated nicotine. You would not want to vape that straight, would make you sick. The strongest you can go is 36mg or 3.6% and even then you would not want to vape more than 3ml a day with juice that strong. Nicotine levels 6mg to 24 mg are typically what people vape. You need to add PG/VG to that as well to bring the nicotine concentration down.