2.5 gallons of liquor for a mix How many 750ml bottles do I need?

There are 3785.41 ml in a gallon, while a 750ml bottle contains 750ml of liquid.

Divide the total volume of liquor by the volume of a single bottle to determine how many bottles are required:

(2.5 gallons * 3785.41 ml / gallon) / 750 ml / bottle = 12.62 bottles

Since you can't buy a fraction of a bottle, you'll need to purchase 13 bottles to have enough liquor for your mix.