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The difference of temperatures between the freezing- and boiling-points of water under standard atmospheric pressure shall be called 100 degrees. (The same increment as the Celsius scale) Thomson's best estimates at the time were that the temperature of freezing water was 273.7 K and the temperature of boiling water was 373.7 K. [33]
For temperature range: 173.15 K to 273.15 K or equivalently −100 °C to 0 °C At triple point. An important basic value, which is not registered in the table, is the saturated vapor pressure at the triple point of water. The internationally accepted value according to measurements of Guildner, Johnson and Jones (1976) amounts to:
Notably, the Kelvin, Celsius, Rankine, and Fahrenheit scales were, or currently are, defined by the freezing and boiling points of water. The less common scales of Delisle, Newton, Réaumur, and Rømer were defined similarly. The triple point of water is a more commonly used standard point today.
Boiling point (°C) K b (°C⋅kg/mol) Freezing point (°C) K f (°C⋅kg/mol) Data source; Aniline: 184.3 ... K f [2] K b [1] Water: 100.00 0.512 0.00 –1.86 K b ...
Kelvin Rankine Fahrenheit Celsius Réaumur Temperature Absolute zero: 0 K 0 °Ra −459.67 °F −273.15 °C -218.52 °Ré Freezing point of brine [a] 255.37 K 459.67 °Ra 0 °F −17.78 °C −14.224 °Ré Freezing point of water [b] 273.15 K 491.67 °Ra 32 °F 0 °C 0 °Ré Boiling point of water [c] 373.1339 K 671.64102 °Ra
Historically, the temperature of the triple point of water was defined as exactly 273.16 K. Today it is an empirically measured quantity. The freezing point of water at sea-level atmospheric pressure occurs at very close to 273.15 K (0 °C).
Empirical scales measure temperature in relation to convenient and stable parameters or reference points, such as the freezing and boiling point of water. Absolute temperature is based on thermodynamic principles: using the lowest possible temperature as the zero point, and selecting a convenient incremental unit.
Moreover, the triple point of water remains one of the 14 calibration points comprising ITS‑90, which spans from the triple point of hydrogen (13.8033 K) to the freezing point of copper (1,357.77 K), which is a nearly hundredfold range of thermodynamic temperature.