## Temperature Conversion Formulas and Online Calculator

Some of the most commonly used instrumentation formulas are the temperature conversion equations. These conversion equations are provided below, with a useful online temperature conversion calculator which will convert between the most commonly encountered temperature scales in the oil and gas, and process industries.

## Kelvin (K)

The Kelvin temperature scale, called after the Scottish physicist and mathematician - Lord Kelvin (William Thompson 1824-1907), is the fundamental temperature scale. He discovered the principal laws governing the behaviour of matter in relation to energy and heat, and this led to the idea of an "absolute zero" i.e. a temperature below which it was impossible to go since matter had zero energy at that point. He used the celsius degree for making his measurements so a 1K difference in temperature is equivalent to a 1°C difference in temperature. The Kelvin temperature scale has been adopted as the SI preferred unit for temperature. Note, that the K for Kelvin does not carry a degree sign.
Enter your value of K and press convert. The equivalent in Celsius, Fahrenheit and Rankine are displayed. As mentioned above, it is physically impossible to have anything colder than zero Kelvin, even although the conversion calculator below allows you to enter negative values of K.

Kelvin

Kelvin to Celsius
=(K+273.15)

Kelvin to Fahrenheit
=(K+273.15)*1.8+32

Kelvin to Rankine
=(K*9/5)

## Rankine (° R)

The Rankine temperature scale, called after the Scottish engineer W J M Rankine (1820-1872) who created the scale, is the Kelvin scale using the Fahrenheit degree instead of the Celsius. So a 1°R difference in temperature is equivalent to a 1°F difference in temperature.
Enter your value of °R and press convert. The equivalent in Celsius, Fahrenheit and Kelvin are displayed.

Rankine

Rankine to Celsius
=(°R*5/9)-273.15

Rankine to Fahrenheit
=°R-459.67

Rankine to Kelvin
=°R*5/9  ## Fahrenheit (° F)

Gabriel Fahrenheit, an instrument maker in Amsterdam, used mercury as the fluid in a thermometer. He calibrated the thermometer to read 212° for the boiling temperature of water and to read 32° for the freezing point of water. This has become known as the Fahrenheit scale.
Enter your value of °F and press convert. The equivalent in Celsius, Kelvin and Rankine are displayed.

Fahrenheit

Fahrenheit to Celsius
=(°F-32)/1.8

Fahrenheit to Kelvin
=(°F-32)/1.8-273.15

Fahrenheit to Rankine
=°F+459.67

## Celsius (° C)

The Celsius temperature scale is called after the Swedish astronomer Anders Celsius (1701-1744) who set the boiling-point of water as his zero mark, and put the freezing-point at 100 degrees. It was reversed a few years later and gained wide popularity, especially with scientists. It became known as the Centigrade scale because of its 100 divisions, however there was also a unit of angular measurement called a "grade" which was sub-divided into "centigrades". To avoid confusion the General Committee on Weights and Measures ruled in 1947 that the word "Celsius" was to be used instead of centigrade.
Enter your value of °C and press convert. The equivalent in Fahrenheit, Kelvin and Rankine are displayed.

Celsius

Celsius to Fahrenheit
=(°C*1.8)+32

Celsius to Kelvin
=°C+273.15

Celsius to Rankine
=(°C*1.8)+491.67

## Technical Library

The following pages on Control and Instrumentation.com give more detail on the techniques used in temperature measurement:   