Degrees Celsius or Centigrade (°C) Unit Definition

The Celsius scale, otherwise known as the centigrade scale, is a temperature scale. As an SI derived unit, it is used worldwide. In contrast in the United States, the Bahamas, Belize, the Cayman Islands and Liberia, Fahrenheit (°F) remains the preferred scale for everyday temperature measurement. The degree Celsius can refer to a specific temperature on the Celsius scale or a unit to indicate a difference between two temperatures or an uncertainty.

The Celsius scale is named after the Swedish astronomer Anders Celsius (1701–1744) Before being renamed to honor Anders Celsius in 1948, the unit was called Centigrade, from the Latin terms centum, which means 100, and gradus, which means steps.

From 1743, the Celsius scale is based on 0 °C for the freezing point of water and 100 °C for the boiling point of water at 1 atmosphere pressure. Prior to 1743, the scale was also based on the boiling and melting points of water, but the values were reversed (in other terms the boiling point was at 0 degrees and the melting point was at 100 degrees). The 1743 scale reversal was proposed by Jean-Pierre Christin.

By international agreement, between 1954 and 2019 the unit degree Celsius and the Celsius scale were defined by absolute zero and the triple point of Vienna Standard Mean Ocean Water (VSMOW), a precisely defined water standard. This definition also precisely related the Celsius scale to the Kelvin (K) scale, which defines the SI base unit of thermodynamic temperature with symbol K. Absolute zero, the lowest temperature possible, is defined as being exactly 0 K and −273.15 °C. Until 19 May 2019, the temperature of the triple point of water was defined as exactly 273.16 K (0.01 °C). This means that a temperature difference of one degree Celsius and that of one kelvin are exactly the same.

On 20 May 2019, the kelvin was redefined so that its value is now determined by the definition of the Boltzmann constant rather than being defined by the triple point of VSMOW. This means that the triple point is now a measured value, not a defined value. The newly-defined exact value of the Boltzmann constant was selected so that the measured value of the VSMOW triple point is exactly the same as the older defined value to within the limits of accuracy of contemporary metrology. The degree Celsius remains exactly equal to the kelvin, and 0 K remains exactly −273.15 °C.

• Absolute zero (exactly): -273.15 °C

• Boiling point of liquid nitrogen: -195.80 °C

• Sublimation point of dry ice: -78 °C

• Intersection of Celsius and Fahrenheit scales: -40 °C

• Melting point of H2O (purified ice): -0.0001 °C

• Room temperature (NIST standard): 20 °C

• Normal human body temperature (average): 37 °C

• Waters boiling point at 1 atm (101.325 kPa) (approximate: see Boiling point): 99.9839 °C

Here are the conversion formulas used to convert both from and to degrees celsius or centigrade:

• Degrees Celsius or Centigrade (°C)
• Degrees Delisle (°De)
• Degrees Fahrenheit (°F)
• Degrees Newton (°N)
• Degrees Rankine (°Ra)
• Degrees Réaumur (°Ré)
• Degrees Rømer (°Rø)
• Kelvin (K)

• Degrees Fahrenheit (°F)
• Kelvin (K)
• Accuracy

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“Celsius.” Wikipedia, Wikimedia Foundation, 30 Mar. 2020, en.wikipedia.org/wiki/Celsius.