How this calculator works
A coffee ratio compares the weight of ground coffee with the weight of water, not the volume of either. Weight is more consistent because a scoop of coffee varies with the grind and how it settles, while a scale gives the same dose every time. Espresso is brewed at a low ratio, from one part coffee to one and a half or two parts water, while filter methods use one part coffee to fifteen or seventeen parts water. The ratio is not the same as the strength in the cup, because the brewer and the grind decide how much of the coffee dissolves, but it is the number a recipe controls. The water figure is given in millilitres, which is close to grams for water, and in cups of 240 mL.
Formula
water = coffee x ratio. coffee = water / ratio. One millilitre of water is taken as one gram, so the ratio is a mass ratio. The preset ratios are 1.5 for a ristretto, 2 for espresso, 3 for a lungo, 8 for cold brew, 10 for a moka pot, 11 for an AeroPress, 12 for a French press, 16.7 for a V60 and 17 for a Chemex. Cups = water (mL) / 240.
Worked example
A double espresso dose of 18 g at a ratio of 1:2 gives 18 x 2 = 36 g of water, which is 36 mL, a typical 36 g espresso yield. The same 18 g through a V60 at 1:16.7 needs 18 x 16.7 = 300.6 mL of water, about 1.25 cups. Working backwards, 300 mL of water at 1:16.7 needs 300 / 16.7 = 18.0 g of coffee.
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Frequently asked questions
Should the ratio use the water poured or the coffee produced?
Recipes usually give the water poured, because that is what you measure. The coffee in the cup is less, because the spent grounds hold on to roughly one to two grams of water for every gram of coffee. A 1:16 pour over produces a cup nearer 1:14 by the time the water retained by the grounds is taken out.
Why is a French press ratio higher than an espresso ratio?
Espresso forces a small amount of water through a fine grind under pressure, so a strong concentrate needs little water. A French press steeps a coarse grind in a lot of water and then filters it, so the same strength of extraction needs a much larger water ratio. The numbers measure the recipe, not a different kind of coffee.
Is a ratio of 1:18 better?
The Specialty Coffee Association uses about 55 g of coffee per litre of water, which is close to 1:18, as the centre of its Gold Cup brew testing. Filter recipes commonly sit between 1:15 and 1:18. Start at the ratio for your brewer and adjust for taste; the calculator lets you set your own.
Should I weigh the coffee or use a scoop?
Weigh it if you can. A tablespoon of ground coffee is roughly 5 to 7 g, but that depends on the grind, the roast and how firmly it is packed, so a scoop can be off by a third. A scale removes that variable and makes the ratio meaningful.