Water Cooling Calculator

Cooling is exponential, so the last few degrees take far longer than the first many.

Temperature after 15 minutes38.6 °C

Time to chill26 minutesIce water bath, 95 °C down to 20 °C

In hours0.43

After an hour2.6 °C

Refrigerator174 minutesambient 4 °C

Freezer54 minutesambient -18 °C

Ice water with salt18 minutesambient -5 °C

Cold running water67 minutesambient 12 °C

Still air, room temperaturenever reaches itambient 20 °C

An ice bath beats the freezer, which surprises people. Still air is a poor conductor and the drink sits in an insulating layer of it; water conducts about twenty times better and convects as well. Salt in the ice is faster still.

The formula

T(t) = ambient + (start - ambient) * e^(-k t)

Cooling is exponential, so it never quite finishes

The rate of heat loss is proportional to the temperature difference, which means a drink loses heat quickly at first and ever more slowly as it approaches the surroundings. It gets most of the way fast: a warm can reaches drinkable in a fraction of the time it would take to reach fridge temperature properly.

Ice water beats the freezer

This surprises people. A freezer is far colder, but still air is a poor conductor and the drink is insulated by the layer of air touching it. Water conducts heat about twenty times better and convects as well, so an ice bath at 0 °C chills roughly three times faster than a freezer at −18. Adding salt to the ice lowers it further and is faster still.

Do not forget it in the freezer

Water expands on freezing, which is unusual and is why a forgotten can splits. The exponential curve is exactly what makes this easy to do: the last few degrees take far longer than the first many, so the drink sits there seeming to make no progress and then freezes.

Recipes are starting points

Ovens run hot or cold by 20 degrees, flour absorbs water differently by season and brand, and the same joint of meat cooks at a different rate depending on its shape rather than its weight. Everything here is a planning figure that gets you close enough to start, and the thermometer, the scales and your own notes from last time are what finish the job.