Temperature Conversions - Kelvin, Celsius, Fahrenheit

You probably don't have a thermometer that has Kelvin, Celsius, and Fahrenheit all listed, and even if you did, it wouldn't be helpful outside of its temperature range. What do you do when you need to convert between temperature units? You can look them up on this handy chart or you can do the math using simple weather conversion equations.

Temperature Unit Conversion Formulas

There's no complicated math required to convert one temperature unit to another. Simple addition and subtraction will get you through conversions between the Kelvin and Celsius temperature scales. Fahrenheit involves a bit of multiplication, but it's nothing you can't handle. Just plug in the value you know to get the answer in the desired temperature scale using the appropriate conversion formula:

Kelvin to Celsius: C = K - 273 (C = K - 273.15 if you want to be more precise)

Kelvin to Fahrenheit: F = 9/5(K - 273) + 32 or F = 1.8(K - 273) + 32

Celsius to Fahrenheit: F = 9/5(C) + 32 or F = 1.80(C) + 32

Celsius to Kelvin: K = C + 273 (or K = C + 271.15 to be more precise)

Fahrenheit to Celsius: C = (F - 32)/1.80

Fahrenheit to Kelvin: K = 5/9(F - 32) + 273.15

Remember to report Celsius and Fahrenheit values in degrees. There is no degree using the Kelvin scale. This is because Celsius and Fahrenheit are relative scales. Kelvin is an absolute scale, so it does not use degree symbols.

Temperature Conversion Table

Example Temperature Conversions

The easiest temperature conversions are between Celsius and Kelvin because their "degree" is the same size. The conversion is a matter of simple arithmetic.

For example, let's convert 58 °C to Kelvin. First, find the proper conversion formula:

K = C + 273
K = 58 + 273
K = 331 (no degree symbol)

Kelvin temperature is always higher than its equivalent Celsius temperature. Also, Kelvin temperature is never negative.

Next, let's convert 912 K to Celsius. Again, start with the proper formula:

C = K - 273
C = 912 - 273
C = 639 °C

Conversions involving Fahrenheit take slightly more effort.

Let's convert 500 K to degrees Fahrenheit:

F = 1.8(K - 273) + 32
F = 1.8(500 - 273) + 32
F = 1.8(227) + 32
F = 408.6 + 32
F = 440.6 °F

Absolute or Thermodynamic Temperature

You know Celsius and Fahrenheit are relative scales, while Kelvin is an absolute scale. But, what does that actually mean?

An absolute scale or thermodynamic scale comes the third law of thermodynamics, where the zero point is absolute zero. The Rankine scale is another example of an absolute scale. Absolute temperature is used in physics and chemistry equations to describe relationships between temperature and other physical properties, such as pressure or volume.

In contrast, a relative scale has its zero relative to some other value. In the case of the Celsius scale, the zero originally was the freezing point of water. Now, it based on a defined triple point of water. The original Fahrenheit zero was the freezing point of a brine solution (salt and water). Today, the Fahrenheit scale (like the Celsius scale) is actually defined using the Kelvin scale. In essence, both Celsius and Fahrenheit are relative to Kelvin.

Sources

• Buchdahl, H. A. (1966). "2. Zeroth law". The Concepts of Classical Thermodynamics. Cambridge U.P.1966. ISBN 978-0-521-04359-5.
• Helrich, Carl S. (2009). Modern Thermodynamics with Statistical Mechanics. Berlin, Heidelberg: Springer Berlin Heidelberg. ISBN 978-3-540-85417-3.
• Morandi, Giuseppe; Napoli, F.; Ercolessi, E. (2001). Statistical Mechanics: An Intermediate Course. Singapore; River Edge, N.J.: World Scientific. ISBN 978-981-02-4477-4.
• Quinn, T.J. (1983). Temperature. London: Academic Press. ISBN 0-12-569680-9.
• World Meteorological Organization. World: Highest Temperature. Arizona State University, retrieved March 25, 2016.