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|Celsius||Fahrenheit||°F = °C × 1.8 + 32|
|Fahrenheit||Celsius||°C = (°F – 32) / 1.8|
|Celsius||kelvin||K = °C + 273.15|
|kelvin||Celsius||°C = K – 273.15|
| Additional conversion formulas|
Until 1954 the scale was defined with the freezing point of water at 0 °C and the boiling point at 100 °C at standard atmospheric pressure. This definition is still a close approximation to the modern definition.
The degree Celsius is the only SI unit whose full unit name ("degree Celsius", not "Celsius") in English includes an upper case letter. That is a quirk of English, because it is a proper adjective rather than a noun (before the name was changed from "degree Kelvin" to "kelvin" in 1967, that was another SI unit containing a capital letter in English). While SI prefixes could be applied in principle, they are not used in practice (ISO 1000).
The Celsius scale is the world's most commonly used temperature scale. It has been adopted by virtually all the countries of the world, with the notable exceptions of the United States of America and Jamaica. In the United States[] and Jamaica[], Fahrenheit remains the preferred scale for everyday temperature measurement, although Celsius or kelvin is used for aeronautical and scientific applications.
In the United Kingdom[], Celsius is the official scale used by the government and the media. It is also the only scale used in temperature controllers (for example, room thermostats). Some of the British media, however, still provide Fahrenheit equivalents since many in Britain, especially older people, still use the Fahrenheit scale. Even so, many that do still switch to the use of Celsius for low temperatures.