The ratio used in stores is 1.4 oz of coffee (coarse ground) per 1 cup of water. When I make cold brew at home I use half a pound of coffee and 6 cups of water, which is a slightly different ratio but it works nice because it’s half a bag of coffee and makes half a gallon of concentrate. Just grind coffee, add cold water, steep 20 hours at room temp, strain. Then you have a double-strength cold brew concentrate.

I know it's 5lbs coffee (ground on french press) and 14 liters of water.

If you want to do the conversion to a pound of coffee, it's about 2.8liters, or 3/4 of a gallon of water.