How to batch cocktails for a party: a calculator for volumes and water

Batching a cocktail means mixing a big jug ahead of time so you can enjoy your own party. It works if you do two things: scale every ingredient by the same factor, and add water, because the dilution a shaker or mixing glass gives you has to be added by hand.

Pick a drink, set your guests and how many each, and the calculator gives you the millilitres for the whole batch, plus a matching alcohol-free jug.