|Units & conversions|
The triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium. The triple point of water (TPW) occurs at a temperature of 273.16 K.
The degree Celsius (°C) is the temperature unit of the International Temperature Scale of 1990 (ITS-90), adopted by the Comité international des poids et mesures (CIPM) in 1989. Historically, the scale was founded on the melting point of water, defined as 0 °C, and on the boiling point of water, defined as 100 °C, under normal atmospheric pressure (101325 Pa). Celsius remains a commonly adopted practical temperature scale. One kelvin is equal to one degree Celsius.
The degree Fahrenheit (°F) is the temperature unit widely used in the United States. On this scale the melting point of ice water is 32 °F and the boiling point is 212 °F.