Great question, we all have to learn this stuff
If you want your final mix to be 18 mg/ml, starting from 20 mg/ml only allows for 10% for flavorings in a final blend. That's good if your flavorings are pretty strong, but if you ever use organic flavorings you might want a bit more room to work.
The below may seem kind of dreary, but I like to provide the full math.
The bold text below is the quick answer.
(final mg/ml = nic_base_mg/ml X fraction_of_nic_base; if you have 20 mg/ml nic base, and use 90% nic base, then you have 20 mg/ml x 0.9 = 18 mg/ml in your final mix)
To get from 48 mg/ml to 20 mg/ml, the math is: 48 mg/ml X ? = 20 mg/ml, ? = 20/48 = 0.42, so you need the 48 mg/ml to be 42% of your final blend.
Since you have 250 ml of the 48 mg/ml, we figure out how much total liquid that gets downmixed to: 250 ml = 0.42 X ?, ? = 250/0.42 = 595 ml total.
We now know that you need to mix that 250 ml of 48 mg/ml into a total of 595 ml final liquid, so the amount of "filler" PG and water is: 595 - 250 = 345 ml.
Quick math check: 250 ml X 48 mg/ml = 12000 mg of nicotine.
12000 mg / 595 [total ml after mixing) = 20 mg/ml final strength
So, 345 ml of filler, 595 total ml of mixed liquid.
If you want to end up with about 1% water, 20 mg/ml, starting from 250 ml of 48 mg/ml, I'd add about 6 ml water (1% of 595 ml), and 345 - 6 = 339 ml of PG.
I normally allow a bit more "headroom", room to play, maybe to add some VG at the end, or in case I need a bit more flavorings. In that case I would downmix the 48 mg/ml to 24 mg/ml. That's still relatively "safe" (many vape 24 mg/ml).
The math for converting from 250 ml of 48 mg/ml to 24 mg/ml is easy:
48 mg/ml X ? = 24 mg/ml.
? = 24/48 = 0.5
We need the 48 mg/ml to be 0.5 (50%) of the final.
250 ml = 0.5 X ?
? = 250/0.5 = 500
We need the final solution to be 500 ml
500 - 250 (ml of 48 mg/ml) = 250 ml of filler.
For 1% distilled water, given the total end product is 500 ml, add 5 ml of water, and 250 - 5 = 245 ml of PG.
Now you have 24 mg/ml, 1% water, nic base. If your final goal is 18 mg/ml, then you will use 75% 24mg/ml nicotine base, and 25% left over for flavorings and plus-up filler (a little more PG, or VG). For a 30 ml batch, you would use 22.5 ml of your 24 mg/ml nicotine base, and 7.5 ml for flavorings and final filler.
I know, too much information, but it gets easy with practice
ever drop $150 at a 5 star restaurant and wonder what the idiot was thinking that gives out stars? Taste is way too subjective to answer you with anything more than "here's what I like"
