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Physics > Unit Conversion > What is Celcius – Definition & Conversion
Unit Conversion

What is Celcius – Definition & Conversion

Introduction to Celcius

Celcius is an important scale for measuring temperature. Furthermore, the temperature refers to how hot or cold something is. We usually represent temperatures in some quantity using some units.

Definition of Celcius

Temperature tends to have different readings on different temperature scales. Furthermore, there are three important temperature scales that are Fahrenheit, Celcius, and Kelvin.

In science, the Celcius scale is used mostly in comparison to other scales. This Celcius scale is divided into 100 equal parts, which are called degrees Celcius (°C). It lies between the freezing point and boiling point of water.


The freezing point of water on this scale is 0 degrees Celcius i.e. 0°C. The boiling point of water is 100°C. This thermometer scale is sometimes also called the centigrade scale because there are 100 Celcius degrees between the two fixed points.

The Celsius temperature scale happens to be a common System International (SI) temperature scale and the official scale is Kelvin. More precisely, experts define this scale by absolute zero and the triple point of pure water.

The triple point of water is defined to be 273.16 K i.e. 0.01 °C or 32.02 °F. The interval between one degree Celcius and one Kelvin are exactly the same. Also, note that the use of the degree does not take place in the Kelvin scale because it is an absolute scale.

The scale name gives honour to Anders Celcius. He was a Swedish astronomer who devised this temperature scale.

Before 1948,  before the renaming of the scale as Celcius, its name was the centigrade scale. However, the terms Celcius and centigrade don’t mean precisely the same thing.

A Centigrade scale has 100-degree units between freezing and boiling of water. Hence, the Celsius scale is the same as the Centigrade scale. The Kelvin scale is another Centigrade scale.

Celcius Temperature Conversions

As one can see with these thermometers, the representation of a particular temperature takes place by different numbers on the three temperature scales.

For example, the freezing point of water is 32°F, 0°C, or 273 degrees Kelvin. As it can be seen that 0°C is actually a much higher temperature than 0 K. But a change of 1 degree Kelvin is equal to a change of one Celsius degree.

In addition, 0°C is a higher temperature than 0°F. But a change of one degree in Fahrenheit is not equal to a change of one Celsius degree. We can convert temperature from one scale to another using these simple equations.

  1. From Celsius to Fahrenheit:

T( in Fahrenheit) = 9/5 × T(in Celsius) + 32

  1. From Fahrenheit to Celsius :

T(in Celsius) = 5/9 × ( T (in Fahrenheit) – 32)

  1. From Celsius to Kelvin:

T(in Kelvin)  = T (in Celsius) + 273.15.

  1. From Kelvin to Celsius:

T(in Celcius) = T ( in Kelvin) – 273.15

  1. Remember that do not say °K. This is not correct.

Also, don’t say ‘degrees, Kelvin.’ This value: 225 K is two hundred twenty-five Kelvins.

Example-1: convert 25.0 °C to Kelvin.

Ans: 25.0 + 273 = 298.0

Essentially we treat 273 as 273.0

Everybody in chemistry knows the true conversion value is 273.15, but usually ignores the decimal portion.

Example-2: convert 375 K to degrees Celsius.

Ans: 375 − 273 = 102 °C

Example-3: Convert −50 °C to Kelvin.

Ans: (−50) + 273 = 223 K

Solved Question for you

Q: Is Absolute Zero Possible?

Ans: Absolute zero is the least possible temperature where nothing could be colder and no heat energy remains possible in a substance. Also, one can say that absolute zero is 0 K on the Kelvin scale, which is a thermodynamic i.e. absolute temperature scale. This is equivalent to –273.15 degrees Celsius.

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