# Water Cooling Calculator

URL: https://speedycalculator.com/calculators/food/water-cooling/
Last updated: 2026-10-30

> The water cooling calculator works out how long hot water (or tea, coffee, soup) takes to cool to a drinkable temperature in a cup – using Newton's law of cooling – or how much cold water to mix in to cool it instantly.

## Inputs

- Method
- Temperature unit
- Starting temperature
- Desired temperature
- Room temperature
- Cold water temperature
- Volume in the cup (ml, cups, fl oz, L, tbsp)
- Cup diameter (top) (cm, in)

## Results

- Time to cool
- Cold water to add
- Final volume (mixing)

## Formula

```
Waiting: t = −ln((T − T_room) ÷ (T₀ − T_room)) ÷ k, k = h × A ÷ (m × c), A = π × (d ÷ 2)² (open top), h ≈ 284 W/(m²·K)
Mixing: cold water = V × (T₀ − T) ÷ (T − T_cold)
```

## Explanation

A wide, shallow cup cools faster than a narrow, deep one because more surface is exposed to the air. Blowing, stirring or pouring between two cups speeds cooling further. Hot drinks above about 65 °C (149 °F) can scald.

### How to use the Water Cooling Calculator

- **Method**
- **Temperature unit**
- **Starting temperature**
- **Desired temperature**
- **Room temperature**
- **Cold water temperature**
- **Volume in the cup**
- **Cup diameter (top)**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Choose waiting or mixing, enter the temperatures, the volume and the cup diameter.

### Inputs explained

FieldWhat to enterMethodChoose one: Let it cool in the cup, Add cold waterTemperature unitChoose one: °C, °FStarting temperatureA numberDesired temperatureA numberRoom temperatureA numberCold water temperatureA numberVolume in the cupUnits: ml, cups, fl oz, L, tbspCup diameter (top)Units: cm, in

### Example values

How the main result changes when **Starting temperature** changes and everything else stays at the example values above:

Starting temperatureTime to cool (min)71.253.6959.2118.7513.1142.516.319021

## Worked example

Inputs — Method: Let it cool in the cup; Temperature unit: °C; Starting temperature: 95; Desired temperature: 60; Room temperature: 21; Volume in the cup: 300 ml; Cup diameter (top): 8 cm.

Results — **Time to cool = 9.2 min**; Cold water to add = 0 ml; Final volume (mixing) = 300 ml.

## FAQ

**How long does boiling water take to cool to drinking temperature?**
About 10 minutes in a wide mug to reach 60 °C, longer in a narrow or insulated one.

**What is the best temperature for hot drinks?**
Around 57–60 °C (135–140 °F) for comfortable drinking.

**How can I cool a hot drink quickly?**
Add a little cold water or milk, or pour it between two cups.