How this calculator works
The plan starts from a drinks per person rate. People tend to drink two in the first hour and about one an hour after that, so a four hour party works out at five drinks per drinker. Each drink is then measured in the units the shop sells: beer in litres and bottles, wine in 750 mL bottles of five 150 mL glasses, spirits in 750 mL bottles of twenty five 30 mL shots, and soft drinks in litres. Ice and cups are planned per guest rather than per drinker, because soft drink drinkers use them too. The numbers do not assume everyone drinks the same thing: entering separate drinker counts for each option is what makes the plan realistic.
Formula
drinks per drinker = party hours + 1. beer (L) = beer drinkers x drinks per drinker x 0.355 L. wine bottles = wine drinkers x drinks per drinker / 5, rounded up. spirit bottles = spirit drinkers x drinks per drinker / 25, rounded up. soft drinks (L) = soft drink drinkers x drinks per drinker x 0.355. ice (kg) = guests x 0.5. cups = guests x 3.
Worked example
For a four hour party with 10 beer drinkers, 8 wine drinkers and 5 spirit drinkers, the rate is 4 + 1 = 5 drinks each. Beer is 10 x 5 x 0.355 = 17.75 L. Wine is 8 x 5 / 5 = 8 bottles. Spirits are 5 x 5 / 25 = 1 bottle. That is 23 beer, 40 wine and 25 spirit drinks, or 88 standard drinks in total. For 20 guests, plan 10 kg of ice and 60 cups and glasses.
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Frequently asked questions
Does one drink mean one standard drink?
The plan counts each serving as one drink. In Canada a standard drink is 13.45 g of alcohol: 341 mL of 5 percent beer, 142 mL of 12 percent wine or 43 mL of 40 percent spirits. The 355 mL beer and 150 mL wine used here are a little larger, so the count is close to one standard drink per serving. Stronger beer, a fuller glass or a mixed drink with more than one shot changes the alcohol in each serving, so treat the count as a starting point.
Should I buy extra?
A little spare is sensible, especially for wine, because bottles are opened and poured unevenly. But buying far beyond the plan means alcohol left over, which has its own risks around the house. Buy to the plan and arrange for safe transport home for anyone who has been drinking.
What about non-drinkers?
Plan soft drinks and water for everyone, not only the people who are not drinking. A water station and a good non-alcoholic option make the party work for drivers, pregnant guests and anyone who simply does not want alcohol.
How long does food and drink stay safe at a party?
Food should not sit out in the danger zone between 4 C and 60 C for more than two hours. Keep cold food on ice, hot food above 60 C, and replace serving dishes rather than topping them up. Alcohol also impairs judgement about food safety, which is another reason to keep the two stations apart.