How many drinks to buy for a party, ice and cups included

How the party drink calculator works

It counts one alcoholic drink per hour for every adult who drinks, plus one extra each, and one non-alcoholic drink per hour for every guest, plus one extra. The alcohol rule is America's Test Kitchen's: drinks = guests × (hours + 1). For non-alcoholic drinks the Princeton alumni catering guide gives 1 to 1.5 per person per hour, more in hot weather, and Plum Deluxe adds one more per guest. That is why the rate goes from 1 to 1.5 when you pick outdoors in summer.

Alcoholic drinks are split by your mix. A 750 ml bottle of wine pours 5 glasses (America's Test Kitchen), a bottle of sparkling wine 6 flutes of 12.5 cl, about 4 fl oz (Nicolas Feuillatte), and one beer is one 12 oz can. For cocktails, US units follow America's Test Kitchen: 2 fl oz of liquor per drink, 12 cocktails from a 750 ml bottle, plus 4 fl oz of mixer each. In metric the calculator uses the International Bartenders Association Cuba Libre, 50 ml of rum and 120 ml of cola, so a 70 cl bottle makes 14. Half the non-alcoholic drinks are water, as the Princeton guide suggests, and the rest is soda and juice, in 8 fl oz servings (250 ml in metric).

Ice follows the calculator from Reddy Ice, the US packaged ice maker: 1 lb per guest to keep drinks cold indoors and 2 lb outdoors, plus 1 lb per guest when ice also goes in the cups. Reddy Ice gives these amounts for a 6-8 hour event, so the party length stops at 8 hours. Cups are 2 per guest (Princeton), because people put a cup down and lose it, plus 10% spare: Samtell, a banquet glassware supplier, suggests 10 to 20%.

These are amounts to buy with a margin so you don't run out, not a target for anyone to drink. If your guests drink little, lower the drinks per hour in the advanced options. Count designated drivers with the non-drinkers.

A worked example: 25 guests for 4 hours

In the US. The calculator opens with 20 adults who drink and 5 non-drinkers, drivers or kids, 4 hours indoors, and a mix of 30% wine, 40% beer, 10% sparkling wine and 20% cocktails.

• Alcoholic drinks: 20 × (4 + 1) = 100, that is 30 glasses of wine, 40 beers, 10 flutes and 20 cocktails
• Wine: 30 ÷ 5 = 6 bottles of 750 ml; sparkling wine: 10 ÷ 6 = 1.7, so 2 bottles
• Beer: 40 cans of 12 fl oz; liquor: 20 ÷ 12 = 1.7, so 2 bottles of 750 ml
• Non-alcoholic: 25 × (4 + 1) = 125 servings of 8 fl oz, or 1,000 fl oz (7.8 gal). Water is half, 500 fl oz: 30 bottles of 16.9 fl oz. Soda is the other half plus 80 fl oz of mixer: 580 fl oz, 9 two-liter bottles
• Ice: 25 × (1 + 1) = 50 lb, 5 bags of 10 lb
• Cups: 25 × 2 plus 10% = 55

Move the same party outdoors in summer and the alcohol stays the same, non-alcoholic drinks rise to 10.9 gal (42 bottles of water and 12 two-liters) and ice to 75 lb, 8 bags.

In the UK and elsewhere. With 40% wine and 30% beer: 8 bottles of wine, 2 of sparkling wine, 30 cans of 330 ml, 2 bottles of spirits of 70 cl, 13 bottles of soft drinks and 11 of water of 1.5 litres, 25 kg of ice in 13 bags of 2 kg and 55 glasses.

Drinks for 10, 20, 30, 50 and 100 guests

US units, 4 hours indoors, 8 guests in 10 drink alcohol, same mix as the US example. Soda in 2-liter bottles, water in 16.9 fl oz bottles.

Guests	Wine + sparkling	Beers	Soda + water
10	3 + 1	16	4 + 12
20	5 + 2	32	7 + 24
30	8 + 2	48	11 + 36
50	12 + 4	80	18 + 60
100	24 + 7	160	35 + 119

Indoors with ice in the cups you need 2 lb of ice per guest: one 10 lb bag for every 5 guests, 2 bags for 10 and 20 for 100. Liquor for cocktails comes to 1 bottle for 10 guests, 2 for 20 or 30, 4 for 50 and 7 for 100.

Bottles, cans and bags of ice

Wine, sparkling wine and liquor come in 750 ml bottles in the US (70 cl for spirits in the UK). Beer is counted as 12 oz cans, one per drink: if you buy 16 oz tallboys or 24 oz cans, enter that size in the advanced options and the count drops. Soda is counted in 2-liter bottles (67.6 fl oz on the label) and water in 16.9 fl oz bottles; change either size if you buy gallon jugs or 12-packs of cans.

Ice is counted in 10 lb bags, the size of the standard ice bag Uline sells to ice plants. Reddy Ice sells 5, 7 and 16 lb bags: enter your bag size and the count follows. Chilling ice goes in coolers and tubs with the drinks; the ice for cups goes in a separate bucket so it stays clean.

The receipt gives cups one by one, so pick the packs that cover them. With your own or rented glassware, the 10% spare covers breakage.

Common mistakes

• Counting every guest as a drinker. Kids, non-drinkers and drivers go in the other field: the calculator gives them soft drinks only, which everyone needs anyway.
• Buying ice only for the cups. Keeping the drinks cold takes at least as much, twice as much outdoors in summer.
• Forgetting cocktail mixers. At 4 fl oz of mixer per cocktail, 20 cocktails add 80 fl oz of soda, already in the bottle count.
• A mix that doesn't add up to 100. The calculator reads it in proportion: 50% wine and 50% beer gives the same result as 25% and 25%. Check the shares if the numbers look odd.
• Treating the amounts as a goal. They are the most you need on hand: unopened bottles keep for another occasion.