How much coffee do you need for a crowd? A batch-brew planner for cups, grams and decaf

Coffee for a crowd goes wrong in two ways. Either the pot runs dry before the dessert is out, or the carafe is still half full at midnight and tastes like a hot plate. Both come from guessing. The fix is plain arithmetic: how many cups, how big, and how many grams of coffee per litre.

Count the cups, then the grams

Set the guest list, how many of them drink coffee and how many cups each will have over the evening. The planner turns that into litres to brew, grams of ground coffee and the number of batches your machine needs. It also lets you set aside a share for decaf, which is worth doing for any evening that runs past dinner.

Why 55 grams per litre is the starting point

The usual guideline for filter coffee, used by the Specialty Coffee Association, is about 55 grams of ground coffee per litre of water, roughly one part coffee to eighteen of water. It gives a cup that is neither thin nor harsh when the water is hot (around 92 to 96 °C at the coffee) and the brew takes roughly four to eight minutes. That is for a cup you drink straight away.

A party cup is different. It sits, it gets milk and sugar, and people drink it after cake. That is why the planner starts at 62 g/L: a little more coffee holds up better. Go to 70 only if most people take milk. Past that, more coffee mostly means more bitterness and more caffeine per cup, not a better pot.

The water you put in is not the coffee you get out

Dry grounds soak up water, about twice their own weight. If you pour 3 litres into a machine with 165 grams of coffee, around 330 ml stays in the filter and you pour less than 3 litres. Plan for that and you will not be short in the last cups. It is also why the planner shows water in and cups poured as separate numbers.

Brew in rounds, not in one giant pot. Two fresh 1.8 litre batches an hour apart beat one 3.6 litre pot that sits.

Keep it hot without cooking it

Brewed coffee does not like waiting. A hot plate keeps heating the pot, and the flavour turns flat and cooked. An insulated jug or carafe does not heat the coffee at all, and a good one keeps it in the drinking range for a few hours. So brew into a pre-warmed insulated jug, put it on the table, and start the next batch when the first is about half gone. If you have no insulated jug, brew smaller batches and more often.

Two small habits help. Rinse the jug with hot water first, so the coffee does not lose heat to cold metal. Keep it covered, because an open jug cools quickly and loses aroma.

Caffeine, decaf and a sensible end to the evening

A mug of filter coffee typically holds around 100 mg of caffeine, about twice a cup of black tea. People who drink three late at night often sleep badly, and some guests are pregnant, sensitive or simply done for the day. That is why a decaf pot, a tea option and a jug of water belong on the table too. If you are planning drinks for the whole evening, make coffee the closing round, not the opener.

Variations

• Cold brew for a hot day. Make a concentrate at about 100 g per litre, steep it in the fridge overnight, then dilute it to taste with water or ice at the party. It needs no machine and keeps for a few days in the fridge.
• A milk table. Warm a jug of milk and put out an oat or other plant option. A third of guests will take milk, so plan for about 40 ml each.

What to look for

If you are buying a brewer or jug for gatherings, the things that matter at any budget are: capacity that matches your usual crowd (a 1.25 litre machine is fine for four, not for twenty); an insulated carafe rather than a hot plate; a full-width showerhead or even spray over the grounds, so a big bed of coffee is wetted evenly; and a machine that brews a full pot in under ten minutes, so a second round is no wait. An urn is worth it only if you host often.