What this calculator does
Cooling follows an exponential curve rather than a straight line. A drink cools fastest when the gap between it and its surroundings is largest, and slows as it approaches the ambient temperature, which is why the last few degrees take disproportionately long.
The consequence is that a drink twice as warm does not take twice as long. Going from 22°C to 5°C in a −1°C fridge takes about 30 minutes; starting from 35°C takes about 40, not 47. The extra 13 degrees adds only ten minutes because the early cooling is so rapid.
The formula
Newton law of cooling gives the time as the natural logarithm of the starting temperature gap divided by the target gap, all divided by a cooling rate constant k. The gaps are measured against the ambient temperature rather than against zero, which is what makes the curve exponential. The constant k depends on the container, the drink volume and whether the surrounding medium is still air, moving air or water.
| Term | Meaning |
|---|---|
| Newton law of cooling | The rate of cooling is proportional to the temperature difference from the surroundings. |
| Cooling constant k | How fast a particular setup cools, in inverse minutes. Higher means faster. |
| Temperature gap | The difference between the drink and its surroundings, which is what drives the rate. |
| Ice bath | Water and ice together, which cools several times faster than a freezer because water conducts heat far better than air. |
The inputs explained
| Field | What to enter |
|---|---|
| Starting drink temperature (°C) | Starting drink temperature in Celsius. |
| Target temperature (°C) | Target temperature. It must be above the ambient temperature, since a drink cannot cool past its surroundings. |
| Cooling environment temperature (°C) | The surrounding temperature: about 4°C for a fridge, −18°C for a freezer, 0°C for an ice bath. |
| Cooling rate constant (k) (1/min) | The cooling rate constant. 0.045 is a reasonable figure for a can in a freezer; an ice bath is considerably higher and still air considerably lower. |
When to use it
Chilling drinks before guests arrive
Knowing whether thirty minutes is enough determines whether the drinks go in the freezer or the fridge.
Comparing chilling methods
An ice bath has a much higher k than a freezer, and running both shows the difference in minutes rather than as an assertion.
Avoiding forgotten bottles
Knowing roughly when a bottle reaches target is also knowing when it is at risk of freezing and bursting if left longer.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How long does chilling take from each starting temperature?
A range of starting temperatures chilled to the same target.
| Starting temperature | Time to chill to target | Starting gap above ambient | Target gap above ambient |
|---|---|---|---|
| 22 °C | 29.9 min | 23.0 °C | 6.0 °C |
| 30 °C | 36.5 min | 31.0 °C | 6.0 °C |
| 35 °C | 39.8 min | 36.0 °C | 6.0 °C |
Questions
What is the fastest way to chill a drink?
An ice bath with water and salt, which beats a freezer comfortably. Water conducts heat far better than air, so a can in ice water cools in a fraction of the time it takes in a freezer, and adding salt lowers the bath below 0°C. Keeping the water moving helps further.
Why does the last few degrees take so long?
Because cooling rate is proportional to the temperature gap, and the gap is smallest at the end. A drink at 8°C in a 4°C fridge is cooling four times more slowly than it was at 20°C, so the final approach drags out.
What cooling constant should I use?
It depends entirely on the setup. Around 0.045 per minute suits a can in a freezer. Still air in a fridge is slower, an ice bath is several times faster, and a large glass bottle is slower than a small aluminium can. The figure is best calibrated by timing one drink and working backwards.
Can I leave drinks in the freezer?
Only briefly, and with a timer. Water expands as it freezes, so a forgotten can or bottle can split, and carbonated drinks are worse because the dissolved gas comes out of solution as it freezes. The calculation gives a rough time to set that timer by.
For ice cream, where freezing is the point, see the ice cream overrun calculator. For planning drinks for an event, see the party drink planner.