What Temp Celsius Does Water Freeze? The Exact Answer
Water freezes at exactly 0 degrees Celsius at standard atmospheric pressure. That value is the defining point of the Celsius scale, where 0 °C is the freezing point and 100 °C is the boiling point of pure water at sea level.
What Affects the Freezing Point
The 0 °C value applies to pure, fresh water at normal air pressure. If you add impurities like salt or sugar, the freezing point drops below zero. This is why salt is spread on icy roads — it lowers the freezing temperature so the ice melts. Ocean water, which contains about 3.5% salt, freezes at roughly -2 °C National Institute of Standards and Technology.
Pressure also plays a small role. At higher altitudes, where air pressure is lower, water can freeze at a temperature slightly above 0 °C, though the difference is tiny for everyday purposes. The Royal Society of Chemistry notes that this value is a fundamental reference in chemistry, used to calibrate thermometers and define phase changes Royal Society of Chemistry.
A quick example: if you leave a bottle of distilled water in a freezer set to -5 °C, it will turn to ice because the temperature is below the freezing point. But if the freezer is set to 1 °C, the water stays liquid.
Key Takeaways
- Pure water freezes at 0 °C at standard atmospheric pressure (sea level).
- Adding dissolved substances (salt, sugar) lowers the freezing point below 0 °C.
- Changes in air pressure have a minor effect on the freezing temperature, noticeable mainly at extreme altitudes.
- The 0 °C value is a fixed calibration point in the Celsius temperature scale.
