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Conversion Formulae

The conversion formula for calculating degrees celsius (°F) from kelvin (K) is as follows:

  • °F = (K x 9/5) - 459.67

The conversion formula for calculating kelvin (K) from degrees celsius (°F) is as follows:

  • K = (°F + 459.67) x 5/9

The Kelvin temperature scale was created in response to the need for an absolute thermometric scale, it has its zero point at absolute zero and progresses from that point.

Kelvin is one of the seven base units of the SI system of units.


The Fahrenheit temperature scale is a non SI temperature scale that is now based on two fixed points, the freezing point of water at 32 °F and the boiling point of water 100 °F.

Unit System

US Customary


1 degree fahrenheit is 1/180th of the interval between the freezing point and boiling point of water. The scale is defined by the freezing point of water at 32 °F and the boiling point of water at 212 °F.

Base Unit


The fahrenheit temperature scale is used in US Customary units and was formerly used in British Imperial units as the main unit of temperature.


Formal: °F


The Fahrenheit temperature scale is names after Daniel Fahrenheit, inventor of the mercury thermomenter, who first proposed the scale in 1724.

Fahrenheit's original scale wasn't based around the freezing and boiling points of water. Some stories say it was based on the lowest temperature to which Farhenheit could reproducibly cool brine (0 degrees) and the average human body temperature (100 degrees), though these would appear to be strange reference points and given that serious research on average human body temperature wasn't done until the 19th century fairly unlikely to be true.

Other sources link the work of Fahrenheit to earlier work done by Ole Rømer, whose temperature scale was based on the freezing point of brine and the boiling point of water.

The Fahrenheit temperature scale was used widely around the world until the mid to late 20th Century when many countries that had previously used Fahrenheit, such as the United Kingdom, Canada, India and Australia, adopted the SI metric Celsius temperature scale.

Global Adoption

Fahrenheit is used in the United States of America, the Bahamas, Belize, the Cayman Islands and US Territories such as Guam, Puerto Rico and the US Virgin Islands.

Conversion Formulae For Conversion To Fahrenheit

  • °F = (°C x 9/5) + 32
  • 32 °F = 0 °C
  • 212 °F = 100 °C


  • °F = (K x 9/5) - 459.67
  • 32 °F = 273.15 K
  • 212 °F = 373.15 K


  • °F = °R - 459.67
  • 32 °F = 491.67 °R
  • 212 °F = 671.67 °R

Conversion Formulae For Conversion From Fahrenheit

  • °C = (°F - 32) x 5/9
  • K = (°F + 459.67) x 5/9
  • °R = °F + 459.67

The kelvin is a measurement unit for temperature defined by having its base at absolute zero, the temperature at which all thermal motion ceases. It is now one of the seven base units of the SI system of units.

Unit System

SI Metric


The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. This formal definition was Resolution 4 of the 13th CGPM (1967/68)

Base Unit


The kelvin is one of the seven base units of the SI metric system.


Formal: K

The abbreviation degrees K or deg K were used prior to Resolution 3 of the 13th CGPM (1967/68), that formally defined the symbol K. (See Resolution 7 of the 9th CGPM (1948) and Resolution 12 of the 11th CGPM (1960) for more information.


The Kelvin scale is named after Northern Irish physicist and engineer William Thompson, 1st Baron Kelvin who identified the need for an absolute thermometric temperature scale in 1848.

Baron Kelvin used the accepted expansion coefficient of gas per degree Celsius (Centigrade in his time) relative to the ice point in order to calculate absolute zero - the base of the scale. His calculation gave a value of -273 °C.

In 1954 Resolution 3 of the 10th CGPM (1954) defined the scale using the triple point of water, with an assigned value of 273.16 K. This definition was further refined in 1967 at the 13th CGPM to the current formal definition.

Global Adoption

Kelvin is used within the scientific community worldwide, including in the United States where Fahrenheit is still in everyday use for weather forecasts.

Conversion Formulae For Conversion To Kelvin

  • K = °C + 273.15
  • 0 K = -273.15 °C


  • K = (°F + 459.67) x 5/9
  • 0 K = -459.67 °F


  • K = °R x 5/9
  • 0 K = 0 °R

Conversion Formulae For Conversion From Kelvin

  • °C = K - 273.15
  • °F = (K x 9/5) - 459.67
  • °R = K x 9/5
Common Conversions °F to K
Common Conversions K to °F
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