How many glasses does a party need? Marked glass or fresh each time, with a glass planner

"How many glasses do I need?" sounds like a counting question: one per guest, plus a few spares. It is really a washing question. The number you need depends on one choice, whether a guest keeps the same glass all evening or gets a fresh one with every drink. Make that choice first and the count follows.

Three ways to use a glass

A fresh glass every time. Easy for guests, hard on you. Every drink adds a dirty glass, so unless you wash during the party you need as many glasses as the party serves drinks. Thirty guests at four drinks each is 120 glasses.

A marked glass for the night. Each guest gets one glass and keeps it. A charm, a strip of tape or a name on a paper label stops the "which one was mine?" shuffle. You only need one glass per guest plus a cushion for the ones that are dropped, lost on a windowsill or taken home by accident.

A new glass when the drink changes. Fizz in a flute, then red wine, then water: each type of drink gets its own glass, and the same glass is reused for more of the same drink. The count sits between the other two, at about one glass per guest for each type of drink they try.

Washing changes the first and third ways. If you can run a dishwasher load or wash a rack by hand while people are still chatting, those glasses come back into circulation and the stock you need shrinks by the size of each load.

Plan your glasses

Set the guests, the drinks each one will have, how many times you can wash during the party, and which way you will serve. The bars compare all three ways at once; tap one to see it as a grid of glasses. The load size and the 10% cushion are my assumptions, not rules: change them to match your own dishwasher and your own guests.

Why a marked glass wins

It is the cheapest way to cover a crowd, and it cuts waste in a quieter way: guests do not abandon half a drink on a shelf and pour a new one. Fewer glasses also means fewer to wash, carry and store afterwards.

The weak point is marking. If the glasses are identical, the marker has to be easy to read in a dim room. Wine charms, a strip of washi tape on the foot, or a pen and a paper label all work. Put a small tray of spare marked glasses by the bar for the first one that gets dropped.

Count the washing, not the guests.

When to break the rule

A marked glass does not suit every drink. Hot drinks need mugs or heatproof glasses. A cold drink poured into a glass that has been warming in a hand tastes warmer sooner, so start each cold drink in a glass that is cool. If you serve a cocktail and a long drink, or fizz and red wine, a second glass type is worth the extra count, and the per-kind way of serving covers exactly that.

Pick sturdier glasses or tough plastic for the garden, a pool edge or a crowded room, and keep a dustpan and a bin for broken glass out of guests' reach.

Water and alcohol-free drinks

Offer water in the same glasses as everything else, in a jug or two on a side table, so nobody feels singled out for choosing it. Treat water and alcohol-free drinks as a kind of drink in the planner above; they add to the count in the per-kind way, not on top of it. Pour sensibly, let people go at their own pace, and keep a way home in mind for every guest.

The short version

Marked glasses: guests times 1.2. Fresh every drink: guests times drinks, less what you can wash during the party. In between: guests times the kinds of drink on offer. Whichever you choose, tell your guests how it works when they arrive, so the glasses can do their job.