How this calculator works
The coffee to water ratio sets how much ground coffee goes into a given amount of water. A French press holds coffee and water together and then filters, so it commonly uses 1 part coffee to 15 parts water; a drip or pour over passes water through a bed of grounds and uses a little more water, around 1 part to 17. Stronger settings add coffee rather than removing water, which keeps the brew time the same and makes the cup more concentrated. Cold brew is different again: it is brewed as a concentrate at 1 part coffee to 8 parts water or less, then diluted with water or milk to drink. The Specialty Coffee Association uses about 55 g of coffee per litre, close to 1:18, as the centre of its Gold Cup testing, so the regular figures here are in the same range.
Formula
ratio = water / coffee, by mass. coffee = water / ratio. water = coffee x ratio. coffee per litre = 1000 / ratio. The regular to strong ratios are 16 to 14 for general use, 15 to 12 for a French press, 17 to 14 for drip or pour over, and 8 to 6 for cold brew concentrate.
Worked example
A French press at the regular ratio of 1:15 with 500 mL of water needs 500 / 15 = 33.3 g of coffee. The same water at the strong ratio of 1:12 needs 500 / 12 = 41.7 g. A drip brewer at 1:17 with 30 g of coffee needs 30 x 17 = 510 mL of water, which is 2.1 cups of 240 mL. At 1:17 the coffee per litre is 1000 / 17 = 58.8 g.
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Frequently asked questions
Is the ratio by weight or by volume?
By weight, because a spoon of coffee varies with the grind and the roast. Water is measured in millilitres, and one millilitre of water weighs one gram, so the water figure doubles as a weight. Use a scale for the coffee and a measuring jug for the water.
Why does cold brew use so much more coffee?
Cold brew is made as a concentrate so that it keeps and can be diluted. At 1:8 the liquid that comes off is very strong; serving it over ice or with water at about 1:1 brings it to a normal drinking strength. Treating cold brew like a drip ratio would make a weak, watery drink.
How do I make the coffee stronger without changing the ratio?
Grind finer or brew longer, which extracts more from the same grounds, rather than adding coffee. Adding coffee makes the brew more concentrated but also changes the balance of flavours, and too fine a grind in a French press makes a muddy cup.
Does the ratio change with the roast?
Dark roasts are more soluble and are often brewed at a slightly higher water ratio to avoid bitterness, while light roasts can take a little more coffee. The ratio is a starting point; taste and adjust the grind and the dose from there.