I went to liquid Xpress.com
I see a 60 milliliter bottle of 36 milligram per milliliter liquid.
I did not see any 60 mg/mL juice.
I believe this is where you're confused.
Many suppliers sell their juice in 30 mL bottles.
This bottle is twice as big, but a drop of 36 mg juice has the same amount of nicotine in it whether it came from a 30 mL, 60 mL or galllon bottle.
The mg is an expression of concentration, the mL is an measure of volume.
So, if you take 1 mL of your 36 mg juice, and cut it with 1 mL of 0 nic anything, you will have 2 mL of 18 mg juice.
Capiche?