What temperature marks the freezing point of pure water at standard atmospheric pressure?

The freezing point of pure water at standard atmospheric pressure is 0 degrees Celsius.

The Celsius scale places water’s freezing point at 0 °C and its boiling point at 100 °C under standard atmospheric pressure. The interval between those reference points is divided into 100 equal degrees, which is why the scale was once called the centigrade scale. In 1948, the international scientific community adopted Celsius as the preferred name.

This value applies to pure water at a pressure of one standard atmosphere. Dissolved substances such as salt lower the freezing point, while changes in air pressure slightly alter the boiling point. Ice and liquid water can also coexist at temperatures near 0 °C, but real weather observations may differ because of impurities, pressure, and measurement conditions. The Celsius scale is used in most countries for weather forecasts and everyday temperatures.