What is Celsius?

The Celsius temperature scale is defined by international agreement in terms of two fixed points; the ice point and the steam point. The temperature of the ice point is defined as 0o Celsius and the steam point as 100o Celsius.

What is Kelvin?

The definition of the Kelvin is the fraction of 1/273.16 of the thermodynamic temperature of the triple point of water. The unit of Kelvin or thermodynamic temperature scale is called the Kelvin.

Lord Kelvin defined a scale based on thermodynamic principles that do not depend on the properties of any particular substance. Kelvin divided the interval between the ice and steam points into 100 divisions so that one kelvin represents the same temperature interval as one Celsius degree.

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Matter around us

Absolute Temperature

The universe has a minimum temperature. That’s not obvious without a better physical interpretation of temperature.

Experiments that measure pressure versus temperature at constant volume and mass produce the same result. Usually, the P-T graphs for different gases have different slopes but they all extrapolate to the same temperature for zero pressure as the V-T plots did for zero volume. Since the smallest possible pressure is zero that temperature intercept is the minimum temperature possible. This is called absolute zero.

The Kelvin scale is based on these experiments. It is not arbitrary, but it is designed so it’s zero point is absolute zero.

0 K = -273.15oC = -459.67oF

The Kelvin (K) is the official metric unit of temperature. Notice there is no “degree” with the kelvin. For example, 3K is called “three kelvins”.

Here is the celsius to kelvin conversion

T = Tc + 273.15

Here is the Kelvin to Celsius conversion

Tc = T – 273.15

The Kelvin scale is designed so one Celsius degree and one kelvin are exactly the same.

Temperature Conversion Factors

The following are the list of conversion formulas

  • Celsius to Kelvin, K = C + 273.15
  • Celsius to Fahrenheit, F = (9/5)C + 32
  • Fahrenheit to Celsius, C = (5/9)(F-32)
  • Fahrenheit to Kelvin, K = (5/9)(F+459.67)
  • Fahrenheit to Rankin, R = F + 459.67
  • Rankin to Kelvin, K = (5/9)R

Base Units of SI system

Three scales are used to measure temperature: the Kelvin, Celsius and Fahrenheit scale. The Celsius scale is sometimes referred to as the centigrade scale, which is an outdated term.

  • The basic unit of temperature in the SI system is the kelvin (K). The Kelvin may be impractical in many cases.
  • The celsius scale is used most often in the clinical laboratory. The kelvin and celsius scales are closely related and conversion between them is simple because the units are equal in magnitude.
  • The difference between the kelvin and celsius scales is the zero point. The zero point on the kelvin scale is the theoretical temperature of no further heat loss, which is absolute zero.
  • The zero point on the celsius scale is the freezing point of pure water. The magnitude of the degree is equal in two scales.

Therefore, water freezes at 273 kelvins, it follows that 0 degrees celsius equals 273 kelvins and that 0 kelvin equals minus 273 degree celsius. Thus to convert from kelvin to degree celsius add 273 to convert from degrees celsius to kelvin subtract 273 as follows.

K = oC + 273

oC = K – 273

Because the celsius scale was devised so that 100oC is the boiling point of pure water, the boiling point on the kelvin scale is 373K.

The following table provides comparative readings of the three temperatures scales, with common reference points.Degrees Celsius

Common reference points on the three temperature scales
Reference point Degrees Fahrenheit Kelvin Degrees Celsius
Boiling point of water 212 373 100
Body temperature 98.6 310 37
Room temperature 68 293 20
Freezing point of water 32 273 0
Absolute zero -459 0 -273

Likewise temperature was not considered to be a basic unit of measure until more recent times. It has now become regarded as one of the fundamental seven units of measure. Simply, temperature is a measure of the relative “hotness” or “coldness” of any object or system.

Solved Example


Ethyl alcohol boils at 78.5oC and freezes at -117oC under a pressure of 1 atm. Convert these temperatures to Kelvin scale.


We have Kelvin = temperature

= Celsius temperature + 273.15

= 78.5 + 273.15

= 351.7 K

Where the answer is read as “351.7 Kelvins”.

Similarly for -117oC ,

Kelvin temperature = -117 + 273.15 = 156K.

Frequently Asked Questions on Celsius to Kelvin

How do you convert Celsius to Kelvin formula?

The conversion of Celsius to Kelvin: Kelvin = Celsius + 273.15. Instead of 273.15 the value of 273 is also used. On this stage consult with your instructor. The following examples will use 273.

Is Negative Kelvin possible?

The particles stop moving at zero Kelvin minus 273 degrees Celsius, and all the disturbance vanishes. So nothing on the Kelvin scale can be colder than absolute zero. In the laboratory, physicists have now produced an atomic gas that has negative Kelvin values though.

Is there an absolute high temperature?

As such, absolute zero is basically when all motion ceases. It reaches temperature at -459.67 degrees Fahrenheit (-273.15 degrees Celsius). We have come to hit this temperature pretty close. As such, the maximum known temperature will tend to be 142 nonillion kelvins (1032 K.).

Why do we use Kelvin instead of Celsius?

Kelvin 0 degrees stands for zero kinetic energy or temperature. Changes in Celsius or Fahrenheit are not directly related to kinetic energy or volume because these scales do not begin at zero. Researchers use the Kelvin scale because it is an absolute scale of temperature which is directly related to kinetic energy and volume.

What is the unit of Kelvin?

The Kelvin, unit of thermodynamic temperature, is the 1/273.16 fraction of the triple point of water’s thermodynamic temperature. The kelvin and the degree Celsius are both the units of the 1990 International Temperature Scale (ITS-90), which the CIPM adopted in 1989.

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