Cost and cup size are straightforward. Brew ratio is a bit trickier. What is it? It's a ratio of water to coffee by weight because you cannot accurately compare dry goods to wet by volume. The ratio is expressed as water:coffee and coffee's value is always 1. So all brew ratios will look something like 15:1, 17:1, etc.
The standard unit of measure used for the ratio is metric. For example:
18:1 means 18 grams of water per 1 gram of coffee
Sound easy enough? You just need a digital scale with gram accuracy and you're good to go!
Our recommended brew ratio is 17:1. It's a great starting point but feel free to adjust to your taste. To make your brew stronger, decrease the water (i.e. 14:1). For a lighter brew, increase the water (i.e. 20:1).
Let's run through two examples to show how to calculate your brew ratio:
(1) Working backward (division). Let's assume you have a 32 oz French press and you want to try a 17:1 ratio. How do you know how much coffee to use? The quickest way to an answer is to simply divide the 32 oz by 17 because the coffee used is 1/17th of the water used. 32/17 = 1.88 ounces of coffee. You can then convert to metric if you wish by multiplying the result by 28.3 (1 oz = 28.3 grams). The full equation looks like this:
32/17 = 1.88 oz x 28.3 = 53 grams coffee
The second way to an answer is by converting to metric first:
32 oz x 28.4 grams = 905.6 grams / 17 = 53 grams coffee
(2) Working forward (multiplication). Let's assume you want to meter your coffee consumption to 1 ounce per day and you want to brew the perfect coffee every time. To start testing ratios, you need to find how much water to use. Simply multiply the weight of coffee you'd like to use (1 ounce in this case) by the ratio of water:
28.3 grams x 17 = 481 grams water