At what temperature does water freeze?

Water freezes at 32 degrees Fahrenheit under standard atmospheric pressure. That is the same temperature as 0 degrees Celsius and 273.15 kelvins, the familiar reference point used to calibrate temperature scales.

The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit in the early 18th century. Fahrenheit originally used a freezing mixture of ice, water, and salt for one reference point, but the scale was later standardized around water’s freezing and boiling points. Pure water freezes at 32°F and boils at 212°F at sea level, creating a 180-degree interval.

The answer describes pure water under ordinary pressure. Dissolved substances change the freezing point: salt lowers it, which is why salt helps melt road ice. Pressure and impurities can also affect the exact phase-change temperature, but those complications do not alter the standard quiz answer. A neighboring fact many people remember is that 32°F equals 0°C, while 212°F equals 100°C.