What is the boiling point of water in degrees Celsius? Water’s commonly stated boiling point is 100 °C.
This value applies to pure water at standard atmospheric pressure, approximately one atmosphere at sea level. Boiling begins when water’s vapor pressure matches the pressure surrounding the liquid, allowing vapor bubbles to form throughout it rather than only at the surface. During steady boiling at constant pressure, added heat mainly drives the liquid-to-gas phase change instead of raising the temperature much further.
Altitude changes the answer because atmospheric pressure decreases higher above sea level. On Mount Everest, water boils at roughly 71 °C, which is why cooking takes longer there. A pressure cooker does the opposite: it raises pressure and allows water to reach a higher temperature before boiling.
The number 100 °C is a familiar rounded value, not a universal constant for every condition. At one atmosphere, the thermodynamic value is about 99.97 °C. At the IUPAC standard pressure of 100 kilopascals, water’s boiling point is about 99.61 °C. The Fahrenheit equivalent of the familiar sea-level value is 212 °F.