Encyclopedia
Kelvin temperature conversion formulas
| Conversion from | to | Formula |
|---|
| Kelvin | Celsius | °C = K - 273.15 |
| Celsius | Kelvin | K = °C + 273.15 |
| Kelvin | Fahrenheit | °F = K × 1.8 − 459.67 |
| Fahrenheit | Kelvin | K = / 1.8 |
| Kelvin | electronvolts | K / 11,604.5 = eV |
| electronvolts | Kelvin | eV × 11,604.5 = K |
Note that for temperature intervals rather than temperature readings,
1 K = 1 °C and 1 K = 1.8 °F
Comparisons among various temperature scales
|
The
Kelvin scale is a temperature scale where absolute zero—the coldest possible temperature where there is no heat energy—is defined as zero kelvin . Its
unit is the
kelvin , which is the SI unit of temperature and is one of the seven SI base units.
The Kelvin scale is named after
British physicist and engineer
William Thomson, 1st Baron Kelvin.
Definition of the kelvin
The unit “kelvin” and its scale are, by international agreement, defined by two points: absolute zero, and the
triple point of specially prepared water. Absolute zero is defined as being precisely 0 K
and –273.15 °C. Absolute zero is where all kinetic motion in the particles comprising matter ceases and they are at complete rest in the “classic” sense. At absolute zero, matter contains no
heat energy. Also, the triple point of water is defined as being precisely 273.16 K
and 0.01 °C. This definition does three things: 1) it fixes the magnitude of the kelvin unit as being precisely 1 part in 273.16 parts the difference between absolute zero and the triple point of water; 2) it establishes that one kelvin has precisely the same magnitude as a one degree increment on the
Celsius scale; and 3) it establishes the difference between the two scales’ null points as being precisely 273.15 kelvins . Temperatures in Kelvin can be converted to other units per the table at top right.
Some key temperatures relating temperatures on the Kelvin and Celsius scales are shown in the below table.
| Point | Kelvin | Celsius | Fahrenheit |
|---|
Absolute zero
| 0 K | –273.15 °C | -459.67 °F |
| Water's freezing point | 273.15 K | 0 °C | 32 °F |
Water’s triple point
| 273.16 K | 0.01 °C | 32.018 °F |
| 373.1339 K | 99.9839 °C | 211.9710 °F |
A For Vienna Standard Mean Ocean Water at one standard atmosphere when calibrated solely per the two-point definition of thermodynamic temperature. Older definitions of the Celsius scale once defined the boiling point of water under one standard atmosphere as being precisely 100 °C. However, the current definition results in a boiling point that is actually 16.1 mK less. For more about the actual boiling point of water, see VSMOW water in temperature measurement.SI prefixed forms of kelvin
SI prefixes are often employed to denote decimal multiples and submultiples of the kelvin. The most commonly used factors of kelvin are listed below.
| Submultiples | | Multiples |
| Factor | Name | Symbol | | Factor | Name | Symbol |
| 10−3 | millikelvin | mK | | 103 | kilokelvin | kK |
| 10−6 | microkelvin | µK | | 106 | megakelvin | MK |
| 10−9 | nanokelvin | nK | | 109 | gigakelvin | GK |
| 10−12 | picokelvin | pK | | 1012 | terakelvin | TK |
Typographical and usage conventions
Uppercase/lowercase and plural form usage
When reference is made to the unit kelvin , kelvin is always spelled with a lowercase k unless it is the first word in a sentence. When reference is made to the Kelvin
scale, use an uppercase K.
Until the 13th General Conference on Weights and Measures in 1967-1968, this unit was called a degree just as other temperature degrees are, distinguished from other degrees with the adjective “Kelvin” in “degrees Kelvin,” or often as “degrees absolute” . When the units were degrees, the plural was formed by adding an “s” to degree and like other adjectives in English, the adjective identifying the scale was unchanged in the plural. After the name change, the plural of kelvin is “kelvins.” When reference is made to the “Kelvin
scale,” the word “kelvin”—which is normally a noun—functions adjectivally to modify the noun “scale” and is capitalized.
Temperatures and intervals
Because the kelvin is an individual unit of measure, it is particularly well-suited for expressing
temperature intervals: differences between temperatures or their uncertainties . Of course, the kelvin is also used to express specific temperatures along its scale . Note that to avoid confusion, especially when temperatures and uncertainties both appear in the same document, the singular form of kelvin is preferred when referring to temperatures; the plural form is preferred when referring to intervals.
One disadvantage of the kelvin is that intervals
and specific temperatures on the Kelvin scale both utilize the exact same symbol . Thus, wherever ambiguity might arise due to the dual use of the symbol K within a document, it is preferable to use the symbol for denoting temperatures and to express the intervals using the full unit name in its plural form,
kelvins,Formatting and typestyle for the K symbol
The kelvin symbol is always a roman capital K since the lowercase version is the SI prefix for 1 × 10
3. The admonition against italicizing the symbol K applies to all SI unit symbols; only symbols for variables and constants are italicized in scientific and engineering papers. As with most other SI unit symbols there is a space between the numeric value and the kelvin symbol . For more information on conventions used in technical writing, see the informative by the
NIST.
The special Unicode kelvin sign
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 “kelvin sign” at U+212A. One types
K when encoding this special kelvin character in a
Web page. Its appearance is similar to an ordinary uppercase K. To better see the difference between the two, below in maroon text is the kelvin character followed immediately by a simple uppercase K:
KKWhen viewed on computers that properly support Unicode, the above line appears as follows :
There is a noticeable difference between the two. However, if the computer being used to view a particular Web page doesn’t support the Unicode kelvin sign character , it may be canonically decomposed by the
browser into U+004B and the two would appear identical. In still other computers, the kelvin symbol is mapped incorrectly and produces an odd character.
Accordingly, for Web use, it is better to use the simple uppercase K to represent the kelvin symbol so it can be properly viewed by the widest possible audience.
Why technical articles use a mix of Kelvin and Celsius scales
In science and in engineering, the Celsius and Kelvin scales are often used simultaneously in the same article This issue had been which stated that
"a temperature interval may also be expressed in degrees Celsius." Yet the practice of simultaneously using both “°C" and “K" remains widespread throughout the technical world as the use of prefixed forms of “°C" has not been well–adopted.
This practice of using both “°C" and “K" is usually avoided in non-technical articles intended for the general public where both the kelvin and its symbol, K, are not well recognized and could be confusing.
See also
References
External links
-
- Barry N. Taylor, Guide for the Use of the International System of Units , Washington, D.C.:Government Printing Office, 1995
