"It depends" is a lame answer, but it definitely applies here. Being prescriptive about some magical correct coffee-to-water ratio is impossible (and anyone telling you they know the answer is just making it up!). It's highly dependent on your ingredients (beans, how they're ground, roasting method, etc.), the brew method (time, fridge vs room temp, type of water, etc.), whether you'll dilute it later with water/milk/ice, and most importantly your individual taste preference. So if you Google it, you'll see an incredibly wide array of opinions about the correct cold-brewing ratio. So our best advice is to use your Rumble Jar or Rumble Go to figure it out yourself. We've included notches (i.e. short horizontal lines) on the sides of our filters as general guides, not as prescriptive tools. They're there to help you eyeball your grounds as you prepare a batch and roughly figure out how much you personally prefer, so you can easily approximate it next time. What we can tell you is that the vast majority of folks prefer to fill their filter with grounds somewhere in between the lower and upper notches, so you can think of that range as the "sweet spot". Rumble Jar: The lower notch is our best guess for where you'll want to start (~1.5 ounces of ground coffee in the quart size and ~3 ounces in the half gallon size). Fill your grounds to that line or just a bit above it, then drink that batch of cold brew and then reassess to figure out whether you want more grounds for your next batch. The higher notch holds ~3 ounces of grounds in the quart size and ~5 ounces in the half gallon size. Some folks like to brew a higher-strength "concentrate" and then dilute it with water/milk/ice when they drink it, so that's an option too if you want to get more cups out of each batch you make.Rumble Go: Given the height-adjustability of the base, the capacity of the filter will change depending on how tall you make your filter. In general, we've found folks brewing in 16-24oz bottles fill the filter with grounds between the lower and middle notch. Folks brewing in 25-32oz bottles fill the filter between the middle and upper notch.