What temperature marks the freezing point of water on the Celsius scale?

On the Celsius scale, the freezing point of water is 0 degrees Celsius.

The scale is based on familiar phase changes of water. At standard atmospheric pressure, pure water freezes at 0 °C and boils at 100 °C. These reference points made the scale practical for science, weather observations, and everyday temperature reporting.

Swedish astronomer Anders Celsius proposed a centigrade temperature scale in 1742. His original arrangement placed the boiling point at zero and the freezing point at 100; later users reversed the scale into the form now used worldwide.

The 0 °C value applies to pure water at standard pressure. Dissolved substances, pressure changes, and supercooling can alter the exact behavior of water. The Celsius scale is used with the kelvin in the International System of Units.