Generally, bottle quantities recommended provide some small overages of wine from 10 oz per guest formula.
"+" sign indicates somewhat less than formula and additional bottle may be desirable to have on hand
Chart #1 - "How many drinks to plan" provides calculations for 4, 6 and 10 people. If your customer is entertaining 20, multiply the drinks shown for 10 people by 2
Chart #2 - "How many drinks per bottle." Here, at a glance, are the number of drinks you can expect (1.5 oz. liquor servings, 5oz wine servings) from a bottle in the various container sizes. Charted for 1 to 12 bottles. Examples: The customer figures he will need for his party 30 drinks of Scotch, 10 drinks of bourbon, about 40 drinks of vodka or gin, The chart translates his needs to bottles as follows: Two 750 mls of Scotch, one 750 ml of bourbon, one 1.75 of vodka (or gin). Use the same way to figure how much wine to buy. Two 3 liter containers of wine will supply 30 wine servings of 5oz. each.
Chart #3 - "How many bottles of table wine to buy" - for 4 to 20 people. Example: If the customer is having 12 people, five 750 mls or 2+ magnums (1.5 liters) are recommended (2 servings of 5 oz each per person).