Difference Between Kelvin and Celsius

Kelvin vs Celsius

Kelvin and Celsius are two units of temperature measurement. Both Kelvin and Celsius are very important unit systems when it comes to fields such as physics, thermodynamics, engineering and astronomy. Both these unit systems are well defined, and have similarities, as well as differences. In this article, we are going to discuss in depth the definitions of Kelvin and Celsius, and their significance, applications, similarities, and differences.


Celsius is a unit system in the measurement of temperature. Temperature is a measurement of the amount of thermal energy stored in an object. Until 1954, the Celsius was defined based on the boiling point and the melting point of water. This is still the definition taught in schools. However, after 1954, scientists came up with a new definition using the absolute zero and the triple point of specially prepared water. In 1742, Anders Celsius, a Swedish astronomer, created a scale with zero as the boiling point and one hundred as the melting point of water. This scale was later reversed to make the Celsius scale. The main significance of using the boiling point and melting point of water under standard pressure, which is the atmospheric pressure at sea level, is that it is a very convenient method to calibrate thermometers such as the Boyle’s apparatus, thermocouple, or even the widely used mercury thermometers. Celsius is not an absolute scale. Later, the definition of the Celsius scale was changed, to be defined by the triple point of water and the absolute zero. The triple point of water is precisely 0.01 °C, while the absolute zero is -273.15 °C. The unit Celsius is now defined as 1/273.16 factor of the temperature difference between the triple point of water and the absolute zero. The unit of Celsius is °C.


The unit Kelvin is named after the physicist William Thomson, 1st baron Kelvin or more commonly known as Lord Kelvin. Kelvin is one of the seven base units in the SI units. Lord Kelvin proposed that there should be a unit system, where the unit size is as same as the Celsius, and the zero of the unit system as the absolute zero. This system was later developed and named in honor of Lord Kelvin. Kelvin is an absolute thermometric scale, which means the amount of thermal heat present in a body is directly proportional to the temperature in Kelvin. The Kelvin uses the triple point and the absolute zero as its defining points. Absolute zero is zero Kelvin and the triple point of water is 273.16 K. In this case, it can be clearly seen that the Celsius and Kelvin are clearly similar in magnitude.

What is the difference between Kelvin and Celsius?

- Kelvin is an absolute unit system, whereas Celsius is not.

- Kelvin can be directly applied to any equation that contains any form of mathematical relationship with temperature, but Celsius, in almost all the cases, must be converted into Kelvin scale.

- Kelvin scale doesn’t have negative values, but Celsius scale has.