What is the temperature at which water freezes on the Celsius scale?

Water freezes at 0 degrees Celsius under standard atmospheric pressure. At this temperature, liquid water and solid ice can exist in equilibrium, with the change of state occurring as water molecules settle into an ordered crystal structure.

The Celsius scale was originally tied to water’s phase changes. Swedish astronomer Anders Celsius proposed a centesimal temperature scale in 1742; its original arrangement placed water’s boiling point at 0 and freezing point at 100. The scale was later reversed into the form used today.

The value is pressure-dependent. At ordinary sea-level pressure, water’s freezing point is 0 °C, but dissolved substances such as salt lower it, which is why salt helps melt icy roads. The frequently confused value of 32 degrees refers to Fahrenheit, while −273 °C is close to absolute zero, not water’s freezing point. Pure water can also remain liquid below 0 °C in supercooled conditions.