Ice is the most consistently under-bought item in home entertaining, and it isn't close. The reason is that hosts picture ice as what goes in the glass, when most of a party's ice does a different job entirely: it's refrigeration. Once you see the two jobs separately, the numbers stop being surprising.
Job one: ice in drinks
The planning figure is 1 lb (0.45 kg) per guest per hour in warm weather — covering iced drinks, melt in the glass, and the ice bucket that keeps getting raided. Cool indoor parties run ~30% less; a hot outdoor afternoon runs 40% more, because melt accelerates and people ice everything.
Job two: chilling bottles and cans
A cooler full of room-temperature drinks needs roughly ice equal to the weight of the drinks in it to chill and hold them. A 24-can slab weighs about 20 lb; it wants about 20 lb of ice. This is the job hosts forget, and it's bigger than job one for any party where the drinks arrive warm from the shop.
Worked examples
| Party | Drinks ice | Cooler ice | Total |
|---|---|---|---|
| 15 guests, indoors, 3h, drinks pre-chilled | 30 lb | 0 | 30 lb (3 bags) |
| 25 guests, warm, 4h, some chilling | 100 lb | 40 lb | 140 lb (14 bags) |
| 50 guests, hot outdoor, 4h, all chilling | 280 lb | 150 lb | 430 lb — order delivery |
Above ~200 lb, stop planning supermarket runs: party ice suppliers deliver 10 and 25 lb bags cheaply in most cities, and one delivery replaces four sweaty car trips.
Technique (this is where parties are won)
- The salt-water bath. To chill 24 warm bottles in ~15 minutes: cooler, ice, water to cover, a large handful of salt. Salt water gets below 0°C and water contact transfers heat ~20× faster than air. Ice alone takes 45+ minutes.
- Fill coolers 30–45 minutes before guests arrive, not as the doorbell rings.
- Separate the drinking ice. Keep one clean bag in the freezer for glasses; the cooler ice that hands have been fishing through all night is not the ice you want in drinks.
- Shade and lids. A closed cooler in shade loses ice at half the rate of an open one in sun. The physics is free; use it.
- Don't drain the cold water — ice-water chills better than ice alone. Drain only when adding fresh stock.
Why not make ice at home?
A domestic freezer produces roughly 1–2 lb per day of tray ice. For a 25-guest party needing 140 lb, you'd need to have started in June. Bagged ice costs a few dollars per 10 lb; it is the single best value item on the entire party shopping list.
The ice calculator runs both jobs — drinks and cooler chilling — for your guest count, weather and hours.