Part science, part arithmetic question.  For alcohol with proof x what volume constitutes a single drink?  Defining a standard drink as 14 grams of alcohol:  https://en.wikipedia.org/wiki/Standard_drink  although it seems to be the wrong units.  I vaguely remember something about moles but wouldn't recall how to apply this here.  Actually, not sure where I got the 14 grams from, but a unit of alcohol looks to be perhaps a better measure:  https://en.wikipedia.org/wiki/Unit_of_alcohol  see also:  How to determine the alcohol content of a mixed-drink? 
The question provided a link to "How to determine the alcohol content of a mixed-drink?", so I'll assume you want a simpler, easier to understand answer.  Consider some common drinks:   12 US fl.oz. (355 mL) bottle of 5% beer = 355×5/100 = 17.75 mL alcohol. 1½ US fl.oz (44.4 mL) shot of 40% bourbon = 44.4×40/100 = 17.76 mL alcohol. 5 US fl.oz (148 mL) glass of 12% wine = 148×12/100 = 17.76 mL alcohol.   Your other link defines an American standard drink as 18 mL of pure alcohol, so it's no coincidence that the examples they gave matched so closely.  Basically all you need is the volume of the alcoholic product in mL and the strength as a percentage, and simply multiply them and divide by 18 to get the equivalent number of standard drinks. 