Okay math lesson, I will show you how the PG 120ml/100mg works out mathimatically, I have pg not vg for mine and I use the same as you 120ml/100mg. I don't use a calculator for mine I figure mine out the old fassion way, I just don't have trust in other peoples calculators I guess. You have to remember everything is done by Volume and adding weight it gets trickey and also just put it into the freezer it doesn't freeze solid like you are thinking. The level is so high for the nicotine it won't freeze. When you calculate volume you should be doing a temperature correction to your fluid anyways and calculators don't do that! So example if fluid is 20 degree you measure out 5ml its not really 5ml it might be 4.5ml and vise versa, if you have lab training I am sure you know what I am talking about.
Ingredients
PG Base Nicotine 100mg/ the ml don't matter because we do it by (Edit: mass to volume), so lets say 120ml (5.4ml is our answer and will always be our answer for 18mg no matter if the bottle has 20ml in it or 1000ml in it (this part is calculated by the masses per ml)
Target Nic is 18mg
target amount is 30ml bottle we want to make (we use a target amount because its our double check)
PG we want 75% VG we want 25% and flavouring we want 5%
PG with Nicotine(100mg/120ml) - Target amount 30ml / (Weight of Nicotine 100mg/Target Nicotine you want 18mg)
= You should get 5.4ml
Our water or PGA is 0 so don't need formula for this because it is 0
VG - (Target amount 30ml*vg % 25% / 100) you should end up with 7.5ml
Flavouring - (Target amount 30ml*Flavour % 5% / 100) you should end up with 1.5ml
PG with no nicotine (This gets a little intense) - ((Target amount 30ml * pg percentage 75%) / 100)-(5.4ml this is your total amount in ml of the nicotine part +1.5ml and this is your flavouring amount) should = 15.6ml
So math will look like this with brackets in place etc
30ml/(100mg/18mg)=5.4ml (Nicotine)
(30ml*25%/100)=7.5ml (VG Base)
(30ml*5%/100)=1.5ml (Flavouring)
((30ml*75%)/100)-(5.4ml+1.5ml)=15.6ml(PG Base)
Add all totals together and you should have 30ml if not something is wrong, and if mixing you have a final volume of 45ml lets say you know something is wrong. Hope it helps you figure it out. Having a specified amount to work with gives you something to check your numbers with. Its the only safe way of calculating volume and makes it easy to spot errors its a double check. Its like in statics class equating equilibrium forces in x and y direction must = 0 that is your check, the specified amount you work towards is your check to make sure its calculated correctly. If you really need the calculation for your vg figured out I can perform them, but it will take me a bit to figure it out but it will be basically the same as what I did above in a 30ml bottle for 18mg you will always be adding 5.4ml to that bottle, when you lower the nic level you will be inserting less. Careful working with that strength, I know the first time I worked with it I wished I had goggles it made my eyes burn. With that bottle you are not far off from being 99.9% pure. You will notice its a dark yellow colour, and when you mix your first batch with it you will notice a yellow tinge and not as dark. That colour is from your nicotine. Hope this helps you and gives you some insight to the math involved, it can get more diffficult than this, but I find this is the easiest method to use.
As far as you menthioning diluting it 120ml/100mg with 120ml more that would be 240ml/50mg yess, but then it might freeze not sure never used anything lower than 100mg, I just put it in the freezer and take out what I need and perform a temp correction and bob is your uncle. and Im not going to get into temp correction it gets pretty involved especially for the nicotine and pg or nicotine and vg mixed together, its a bit of fluid dynamics with mass calculations and a refractometer.
