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For other uses, see Celsius (disambiguation).
Celsius temperature conversion formulas
| Conversion from |
to |
Formula |
| 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
Conversion calculator for units of temperature |
Celsius is, or relates to the Celsius temperature scale. Degrees Celsius (symbol: °C) refers to a specific temperature on the Celsius temperature scale. The degree Celsius is also a unit increment of temperature for use in indicating a temperature interval (a difference between two temperatures or an uncertainty). “Celsius” is named after the Swedish astronomer Anders Celsius (1701 – 1744), who first proposed a similar system two years before his death.
Until 1954, 0 °C on the Celsius scale was defined as the melting point of water and 100 °C was the boiling point of water under a pressure of one standard atmosphere. By international agreement, the Celsius scale is now defined at the following two points: absolute zero, and the triple point of specially prepared (VSMOW) water. Absolute zero is defined as being precisely −273.15 °C. The triple point of water is defined as being precisely 0.01 °C.
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Contents
- 1 History
- 2 Uppercase spelling
- 3 Temperatures and intervals
- 4 The freezing and boiling points of water
- 5 World-wide adoption
- 6 The special Unicode °C character
- 7 See also
- 8 Notes
- 9 External Links
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History
A thermometer calibrated in degrees Celsius. The blue zone denotes freezing temperatures.
In 1742, Anders Celsius (1701 – 1744) created a “backwards” version of the modern Celsius temperature scale whereby zero represented the boiling point of water and 100 represented its freezing point. In his paper Observations of two persistent degrees on a thermometer, he recounted his experiments showing that the freezing point of water was effectively unaffected by pressure. He also determined with remarkable precision how water’s boiling point varied as a function of atmospheric pressure. He proposed that zero on his temperature scale (water’s boiling point) would be calibrated at the mean barometric pressure at mean sea level. This pressure is known as one standard atmosphere. In 1954, Resolution 4 of the 10th CGPM (the General Conference on Weights and Measures) established internationally that one standard atmosphere was a pressure equivalent to 1,013,250 dynes per square centimetre (101.325 kPa).
In 1744, coincident with the death of Anders Celsius, the famous botanist Carolus Linnaeus (1707 – 1778) proposed [1] reversing Anders Celsius’ temperature scale so that zero represented the freezing point of water and 100 represented its boiling point. In fact, Linnaeus received his custom-made “linnaeus-thermometer” for use in his greenhouses that same year from Daniel Ekström, Sweden’s leading maker of scientific instruments at the time. As often happened in this age before modern communications, numerous physicists, scientists, and instrument makers had independently developed this same scale;[2] among them were Per Elvius the Elder from Sweden in 1710, Christian of Lyons in 1743, Daniel Ekström, and Mårten Strömer (1707 – 1770) who had studied astronomy under Anders Celsius. For the next 204 years, the unit increment of this scale was known variously as the “centesimal degree,” “degree centigrade,” “degree Celsius,” or simply “degree”. The 9th CGPM formally adopted “degree Celsius” in 1948.
Uppercase spelling
The degree Celsius is the only SI unit whose full unit name (“degree Celsius”) in English includes an upper case letter. Before the “degree Kelvin” was changed to “kelvin” in 1967, it also contained a capital letter in English.
Temperatures and intervals
Besides expressing specific temperatures along its scale (e.g. “Gallium melts at 29.7646 °C” and “The temperature outside is 23 degrees Celsius”), the degree Celsius is also suitable for expressing temperature intervals: differences between temperatures or their uncertainties (e.g. “The output of the heat exchanger is hotter by 40 degrees Celsius,” and “Our standard uncertainty is ±3 deg C”). This dual usage is sanctioned by Resolution 3 of the 13th CGPM (1967/68) which stated that “a temperature interval may also be expressed in degrees Celsius” and is is governed by Resolution 7 of the 9th CGPM (1948) which stated “To indicate a temperature interval or difference, rather than a temperature, the word ‘degree’ in full, or the abbreviation ‘deg’ must be used.”
Note that it is acceptable to denote a temperature in the form “degrees Celsius.” Thus, to avoid confusion whenever both temperatures and intervals appear in the same document, “°C” is preferred when referring to temperatures, and any one of the following should be used to denote the intervals: “degrees Celsius,” “degrees C,” “deg Celsius,” or “deg C” .
In science (especially) and in engineering, the Celsius and Kelvin scales are often used simultaneously in the same article (e.g. “…its measured value was 0.01023 °C with an uncertainty of 70 µK…”) Notwithstanding the official endorsements of Resolution 3 of the 13th CGPM (1967/68)] and Resolution 7 of the 9th CGPM (1948), the practice of simultaneously using both “°C” and “K” remains widespread throughout the technical world as the use of SI prefixed forms of “degrees C” (such as “µ deg C” or “millidegrees Celsius”) to express a temperature interval has not been well-adopted.
The freezing and boiling points of water
The effect of defining the Celsius scale at the triple point of VSMOW water (273.16 kelvin and 0.01 °C), and at absolute zero (zero kelvin and –273.15 °C), is that both the freezing and boiling points of water under one standard atmosphere (1013.25 mbar) are no longer the defining points for the Celsius scale. In 1948 when the 9th General Conference on Weights and Measures (CGPM) in Resolution 3 first considered using the triple point of water as a defining point, the triple point was so close to being 0.01 deg C greater than water’s known melting point, it was simply defined as precisely 0.01 °C. However, current measurements show that the triple and melting points of VSMOW water are actually very slightly (<0.001 deg C) greater than 0.01 deg C apart. Thus, the actual melting point of water is very slightly (less than a thousandth of a degree) below 0 °C. Also, defining water’s triple point at 273.16 K precisely defined the magnitude of each 1 °C increment in terms of the absolute thermodynamic temperature scale (referencing absolute zero). Now decoupled from the actual boiling point of water, the value “100 °C” is hotter than 0 °C — in absolute terms — by a factor of precisely or (approximately 1.3661). Thus, the boiling point of VSMOW water under one standard atmosphere of pressure is actually 373.1339 K (99.9839 °C) when adhering strictly to the two-point definition for calibration. When calibrated to ITS-90 (a calibration standard comprising many definition points and commonly used for high-precision instrumentation), the boiling point of VSMOW water is slightly less, about 99.974 °C.[3]
This boiling–point difference of 16.1 millikelvins (thousandths of a degree Celsius) between the the Celsius scale’s original definition and the current one (based on absolute zero and the triple point) has little practical meaning in real life because water’s boiling point is extremely sensitive to variations in barometric pressure. For example, an altitude change of only 28 cm (11 inches) causes water’s boiling point to change by one millikelvin.
World-wide adoption
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. In broadcast media it was still frequently referred to as centigrade until the late 1980s or early 1990s, particularly by weather forecasters on European networks such as the BBC, ITV, and RTÉ. In the United States, Fahrenheit remains the preferred scale for everyday temperature measurement, although Celsius or kelvin is used for aeronautical and scientific applications. In Jamaica, a conversion to Celsius is taking place.
The special Unicode °C character
Unicode, which is an industry standard designed to allow text and symbols from all of the writing systems of the world to be consistently represented and manipulated by computers, includes a special “°C” character at U+2103. One types ℃ when encoding this special character in a Web page. Its appearance is similar to the one synthesized by individually typing its two components (°) and (C). To better see the difference between the two, below in brown text is the degree Celsius character followed immediately by the two-component version:
℃°C
When viewed on computers that properly support and map Unicode, the above line may be similar to the the line below (size may vary):
Depending on the operating system, Web browser, and the default font, the “C” in the Unicode character may be narrower and slightly taller than a plain uppercase C; precisely the opposite may be true on other platforms. However, there will usually be a discernible difference between the two.
See also
- Absolute zero
- Fahrenheit
- ITS-90
- Kelvin
- Temperature
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- Temperature conversion formulas
- Thermodynamic temperature
- Section: History of thermodynamic temperature
- Triple point
- VSMOW (Vienna Standard Mean Ocean Water)
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Notes
- ^ Citations: Thermodynamics-information.net, A Brief History of Temperature Measurement and; Uppsala University (Sweden), Linnaeus’ thermometer
- ^ Citation for Daniel Ekström, Mårten Strömer, Christian of Lyons: The Physics Hypertextbook, Temperature; Citation for Christian of Lyons: Le Moyne College, Glossary, (Celsius scale)
- ^ Citation: London South Bank University, Water Structure and Behavior, notes c1 and c2
External Links
- NIST, Basic unit definitions: Kelvin
- The Uppsala Astronomical Observatory, History of the Celsius temperature scale
- London South Bank University, Water, scientific data
- BIPM, SI brochure, section 2.1.1.5, Unit of thermodynamic temperature
Temperature scales
| Celsius |
Fahrenheit |
Kelvin |
| Delisle |
Leiden |
Newton |
Rankine |
Réaumur |
Rømer |
| Conversion formulas |
Categories: SI derived units | Units of temperature
