The formula
Every drinks calculator, including the one on the bar page, rests on three numbers you should know you are choosing:
- Who drinks. Not every adult guest drinks alcohol. Planners commonly assume around 85 %; a family-heavy or religious crowd can be much lower.
- How much per hour. The usual rule of thumb is two drinks in the first hour and one per hour after, per drinking guest. The first hour is higher because cocktail hour starts thirsty.
- What they drink. The mix decides how many bottles of each thing you buy.
So: drinks = drinking guests × (2 + hours − 1). For 100 guests, 85 drinking, a 5-hour reception: 85 × 6 = 510 drinks.
Worked example: 100 guests, 5 hours, full bar
With a 30 % beer, 45 % wine and 25 % spirits mix, those 510 drinks are 153 beers, 230 glasses of wine and 127 spirit pours. In US units:
| Item | Buy | How it was worked out |
|---|---|---|
| White wine | 21 bottles | 45 % of wine drinks, 5 glasses of 5 oz per bottle |
| Red wine | 19 bottles | 40 % of wine drinks |
| Rosé | 7 bottles | 15 % of wine drinks |
| Beer | 7 cases of 24 | 153 beers, rounded up |
| Vodka | 3 bottles (750 ml) | 35 % of spirit pours, 16 pours a bottle |
| Whiskey / bourbon | 2 bottles | 20 % |
| Gin | 2 bottles | 20 % |
| Tequila | 2 bottles | 15 % |
| Rum | 1 bottle | 10 % |
| Sparkling for the toast | 13 bottles | 100 guests ÷ 8 pours a bottle |
| Sparkling juice | 2 bottles | for the 15 non-drinkers’ toast |
| Ice | 300 lb | 1.5 lb per guest for drinks + the same to chill bottles |
| Limes / lemons | 16 / 8 | 1 lime per 8 spirit drinks, lemons for half as many |
| Mixers | 10 × 2 L bottles | about 4 oz of mixer per spirit drink |
Why 16 pours from a 750 ml bottle when 750 ÷ 44 ml is nearly 17? Free-pouring and spillage. The calculator takes 5 % off every spirit bottle so you don’t run dry at 10 pm.
At example retail prices (wine around $10, liquor $20, a case of beer $28) the drinks, mixers and ice come to roughly $1,270 — about $13 a guest. Your prices will differ; change them in the mobile bar pricing tool if you want a costed list.
For other sizes, the computed pages give the full list: 50 guests, 75, 100, 150, 200 and 250 guests.
Serving sizes: US, UK and Australia
The same party needs different bottles in different countries, because a “glass” isn’t the same size.
| US | UK | Australia | |
|---|---|---|---|
| Wine glass | 5 fl oz (148 ml) | 175 ml (or 125 ml) | 150 ml |
| Glasses per 750 ml bottle | 5 | 4 (or 6) | 5 |
| Spirit pour | 1.5 fl oz (44 ml) | 25 ml (or 35 ml) | 30 ml |
| Spirit bottle | 750 ml | 70 cl | 700 ml |
| Pours per bottle (after spillage) | 16 | 26 | 22 |
| Beer | 12 oz, cases of 24 | 330 ml, cases of 24 | 375 ml, cartons of 24 |
The US figures are the NIAAA standard drink: 12 oz of regular beer, 5 oz of table wine or 1.5 oz of distilled spirits each contain about 14 g of alcohol. In the UK, gin, rum, vodka and whisky sold by the measure must be served in 25 ml or 35 ml (or multiples), and still wine by the glass in 125 ml or 175 ml (or multiples), under the specified quantities on GOV.UK. Australia defines a standard drink as 10 g of alcohol; a 30 ml nip of spirits is about one.
For 100 guests over 5 hours, UK units mean 58 bottles of wine (more, because the glasses are bigger) and only 6 bottles of 70 cl spirits (fewer, because the measures are smaller).
Adjusting the defaults
Time of day. A lunch reception or a daytime garden party drinks noticeably less than an evening dance party. Try 1.5 drinks in the first hour and 0.75 after.
Crowd. Younger guests and big friend groups push spirits and beer up; older guests and families push wine and soft drinks up. If a third of your guests won’t drink, set the share to 65 %.
Season. Hot days need more beer, more ice (the calculator adds 50 % on a hot day), more water and lighter wines; winter weddings lean to red wine and spirits.
Beer and wine only. Dropping spirits is cheaper, simpler and faster to serve. With a 40 % beer, 60 % wine split, 100 guests over 5 hours need about 63 bottles of wine and 9 cases of beer, and no cocktail mixers.
Signature cocktails. One or two signature drinks reduce the spirit variety you need: put more weight on the base spirit and fewer bottles of everything else.
Kegs or cases?
A half-barrel keg holds 15.5 US gallons, about 165 12 oz beers; a sixth-barrel about 5.16 gallons, roughly 55. In the UK an 11-gallon keg is 88 pints; in Australia a 50-litre keg is the common size. Kegs are cheaper per serving and create less waste, but you need a tap, something to keep the keg cold, a deposit, and someone who knows how to pour. For 100 guests a single half-barrel covers the beer; for 200 or more, kegs usually make sense.
Don’t forget the non-alcohol side
The list includes soft drinks and water for everyone — about a third of a litre per non-drinker per hour, and half a serving per hour for drinkers. Free water all evening is good hospitality and good sense. Anyone running the bar should refuse service to guests who are drunk or under the legal drinking age; if you are using a dry-hire bar, agree that policy with them in advance.
Buying tips
- Ask about returns before you buy. Some shops take back unopened bottles; many don’t, and some US states don’t allow it at all.
- Buy wine by the case. Many shops discount 12-bottle cases or mixed cases.
- Order ice for delivery on the day and keep it out of the sun. Running out of ice is more common than running out of wine.
- Chill early. Bottles take hours to chill in a tub of ice and water; start in the morning.
- Label the bar. A short menu speeds up service and steers guests to what you bought most of.
The shopping list calculator does all of the above for your guest count, hours and mix, prints a checklist, and exports a spreadsheet you can send to your bar company. If you are hiring a mobile bar, read dry hire vs full service first, and put the bar in your wedding budget.