Cold brew's flavor and strength come down almost entirely to one number: the ratio of coffee to water. This calculator turns that ratio into an exact amount of coffee to weigh out for your batch, and helps you figure out how much to dilute the finished concentrate before serving.
How the ratio drives strength
Cold brew ratios are almost always written as coffee-to-water by weight, like 1:4 or 1:8. The first number is always 1 part coffee; the second is how many parts water you steep it in. A 1:4 ratio produces a much stronger, more concentrated brew than a 1:8 ratio made with the same amount of water — because the same amount of coffee is extracting into less liquid.
Because water is close enough to 1 gram per milliliter at room temperature, this calculator treats your water volume (in mL) as the water weight directly, then divides by the ratio to get the grams of coffee needed.
Concentrate ratios vs. serving strength
Most cold brew recipes are brewed strong (1:4 to 1:6) specifically because the concentrate is meant to be diluted before drinking — brewing this way lets you make one batch and adjust the final strength per serving, rather than committing to one strength for the whole batch. Ratios of 1:7 or 1:8 are brewed closer to ready-to-drink strength and need little or no dilution.
The Dilution Guide tab lets you pick any serving size and dilution ratio to see exactly how much concentrate and water (or milk) go into each glass, and how many servings your batch will yield.
Limits and edge cases
This calculator assumes a standard steep (12–24 hours, room temperature or refrigerated, coarse grind) and treats concentrate yield as roughly equal to the water you started with — in practice you'll lose a small amount of liquid to grounds absorption, so real yield will be very slightly less. It doesn't account for altitude, water mineral content, or grind size beyond the standard coarse recommendation, all of which can shift extraction. If you're scaling a specific recipe rather than starting from a ratio, use the ratio that recipe specifies rather than guessing.