I start with a 3:1 ratio of water to grounds, maybe 4:1 by the time it mixes. I do mine in a mason jar, so I fill the jar to 500ml with grounds then I fill that up the rest of the way with water. Its a 1.75L jar so I figure about 1500ml water goes in as its mixing up with the grounds.
Let sit for a day in the fridge and stir or shake occasionally.
This makes a good concentrate, which I then mix with water to get the right taste.