There are 2 factors that go into determining a standard drink: Amount and Strength. A standard drink of beer is 12 oz at 5% Alcohol by volume. This equates to approximately 14 grams of alcohol per drink, and can be transferred over to wine and spirits as well.
Liquor: Mixed drinks have a 1.5-ounce (45 ml) serving of liquor per drink, so a 750-ml bottle will make about 16 drinks. To figure out how many bottles you need, just divide the number of liquor drinks needed by 16.