Pick concentrate or ready-to-drink, set your ratio and batch size, and get exact coffee and water. Grounds vary too much in volume to scoop — weight is how good cold brew stays consistent.
Strong concentrate — dilute before drinking.
Target brew volume
Parts water or milk per part concentrate, for the yield estimate below.
Concentrate uses a strong ratio around 1:5 to 1:8, so a small batch stores compactly and you dilute each glass to taste with water, milk, or over ice. Ready-to-drink brews weaker, around 1:15 to 1:17, so it pours straight from the jug. Both are the same technique at different strengths — pick by how you like to serve it.
Coffee grounds vary enormously in density by roast, grind, and bean, so a "cup of grounds" isn't a fixed amount of coffee. Ratios by weight give the same strength every time. A cheap kitchen scale is the difference between reproducible cold brew and rolling the dice each batch.
Coarse grind, like raw sugar, keeps extraction even and filtering easy — fine grinds cloud the brew and clog filters. Twelve to eighteen hours suits most setups, shorter at room temperature, longer in the fridge. Longer isn't linearly stronger: past a day, harsh woody notes creep in.
Undiluted concentrate keeps well refrigerated for up to two weeks; diluted cold brew is best within a few days as its flavor fades faster. Brew concentrate and dilute per glass if you want it to last.