What most DiY folks do is buy a higher content nic liquid then cut it down. Since i'm not a math wiz the simplest explanation if like this. If you have 36mg juice then you can cut it one for one with PG or VG and end up with 18mg juice. So if you took a 6ml bottle and added 3ml of 36mg juice and 3ml of PG and or VG then you would wind up with 6mls of 18mg juice. That doesn't add in flavoring though. Basically just use the ejuice calculator. lol It takes all the math work and guess work out of cutting it down.