Iced Coffee Dilution Calculator
Brew coffee straight onto ice: enter your dose, ratio and ice weight to get the hot water to brew with so the melt lands at full strength.
How it works
Total water = dose × ratio · Hot water = total water − ice weight
Flash-brewed (Japanese-style) iced coffee brews hot straight onto ice so the coffee chills instantly and keeps its aromatics. The trick is that the ice becomes part of the recipe water: you brew with less hot water because the melting ice makes up the rest. Subtract the ice weight from the total water your ratio calls for to get how much hot water to pour, and the finished drink lands at full strength rather than watery.
Worked example
At a 1:15 ratio, 30 g of coffee wants 450 g of total water. Put 150 g of ice in the cup and you brew with just 450 − 150 = 300 g of hot water — the ice melts to fill the gap.
Frequently asked questions
Why not just pour hot coffee over ice?
If you brew a full-strength batch and then add ice, the melt dilutes it and you get weak iced coffee. Accounting for the ice as part of the water — brewing stronger with less hot water — keeps the final drink balanced.
How much of the water should be ice?
Commonly around one-third of the total water is loaded as ice. That is enough to chill the brew quickly while leaving enough hot water to extract properly. This calculator lets you set the ice weight directly.
Is this the same as cold brew?
No. Cold brew steeps grounds in cold water for many hours. Flash brewing is hot brewing done directly onto ice, so it is ready in minutes and tastes brighter and more aromatic.
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This calculator is for educational purposes. Double-check important results before acting on them.