Calculation for PG, VG and nicotine

[Mr Ripple]

It's 15 ml of flavor not 15%.Also, i have 70ml of 20mg/ml nic boosters and i want to use it with 38mg/ml nic for the final liquid.

It's not possible to get the final vg/pg ratio you want with what you've got unless your flavouring is also suspended in a 50/50 vg/pg mix.

 

[Richard Winter]

The flavor concentrate is 25%.I want to use both 20 mg/ml nic and 38 mg/ml nic.

If you want your flavour to be a 25% strength, which does seem pretty high AND if you want to combine both your nicotine strengths then as @StrawberryRipple has said, you wont get a 50/50 ratio.
You would have to lower the flavour percentage or not combine the two nicotines but use the 3.8% one.

 

[Richard Winter]

One other thing, you said your 3.8% nic is a 50/50 base mix but I'm guessing your 2% nic isn't. You've got quite a lot of variable your juggling with to get a specific mix.