Last Updated: July 2, 2024


The Kelvin scale is a fundamental temperature scale in physics, named after Lord Kelvin. It starts at absolute zero, the theoretical point where all molecular motion ceases, marked as 0 Kelvin (K). Unlike Celsius and Fahrenheit, Kelvin does not use degrees and directly correlates with Celsius for scientific accuracy: 0°C equals 273.15 K. This scale is essential in fields ranging from theoretical physics to practical applications in various technologies, providing a precise measurement system that is crucial for scientific calculations across the globe.

What is Kelvin?

Kelvin is a unit of temperature in the International System of Units (SI), symbolized as K. It is named after the British physicist Lord Kelvin. This scale measures temperature beginning at absolute zero, where all thermal motion ceases, defined as 0 Kelvin. Unlike Fahrenheit or Celsius, it does not use degrees, making it crucial for scientific and engineering calculations. The Kelvin scale is pivotal in fields such as physics, chemistry, and space science, where precise temperature measurements are essential.

Kelvin Scale Formula

The Kelvin scale is directly related to the Celsius scale with a simple formula to convert temperatures between them. Here’s the formula for converting Celsius to Kelvin:

K = C+273.15


  • K is the temperature in Kelvin,
  • C is the temperature in Celsius.

This formula shows that Kelvin and Celsius scales are offset by 273.15 degrees. This means that 0 degrees Celsius, which is the freezing point of water, corresponds to 273.15 Kelvin. Absolute zero, the theoretical minimum temperature, is 0 Kelvin, which equals -273.15 degrees Celsius.

How to Convert a Temperature from Celsius to Kelvin

Converting a temperature from Celsius to Kelvin is straightforward. Here’s the simple step-by-step process:

  1. Start with your Celsius temperature. This is the temperature you want to convert to Kelvin.
  2. Add 273.15 to your Celsius temperature. This conversion factor adjusts for the difference in starting points of the two scales—Celsius starts at the freezing point of water (0°C), whereas Kelvin starts at absolute zero.
  3. The result is the temperature in Kelvin.

Here’s the formula you use for the conversion:

𝐾 = 𝐶+273.15


If you have a temperature of 25°C and want to convert it to Kelvin: 𝐾=25+273.15=298.15 K

Now, you have converted 25°C to Kelvin, which is 298.15 K. This method is used in all scientific contexts where Kelvin is the preferred unit of temperature measurement.

Relation Between Celsius and Kelvin

AspectCelsius (°C)Kelvin (K)
Unit NameNamed after Anders CelsiusNamed after Lord Kelvin
Zero PointRepresents the freezing point of waterRepresents absolute zero
Scale TypeRelative temperature scaleAbsolute temperature scale
Unit IncrementEach increment is equal to 1°CEach increment is equal to 1K
Common UsageWidely used in daily life and weather reporting globallyPredominantly used in scientific and engineering contexts
Base Reference for Zero0°C is the freezing point of water0 K is the lowest possible temperature, where molecular motion stops
Conversion Formula𝐶 = 𝐾−273.15𝐾 = 𝐶+273.15

Absolute zero in Kelvin

Absolute zero is the theoretical lowest temperature possible, where all molecular motion ceases. In the Kelvin temperature scale, absolute zero is defined as exactly 0 Kelvin (0 K). This temperature corresponds to -273.15 degrees Celsius and -459.67 degrees Fahrenheit. Absolute zero is a cornerstone in the fields of physics and chemistry, particularly in understanding the behavior of gases and the laws of thermodynamics.

Scale of the Kelvin


The Kelvin scale is an absolute temperature scale used primarily in the scientific community worldwide. Here are some key characteristics and the scale points associated with it:

Absolute Zero: 0 Kelvin (K) – This is the starting point of the Kelvin scale, representing the lowest possible temperature where all thermal motion of atoms theoretically ceases.

Triple Point of Water: 273.16 K – This is a unique temperature where water can exist simultaneously in gas, liquid, and solid states. This specific point is used to define the Kelvin scale.

Increment: The scale increments by 1 Kelvin, which is equivalent to 1 degree Celsius in magnitude. This means that the temperature interval or thermal unit size is the same as that of the Celsius scale, but the Kelvin scale starts at absolute zero.

Usage: Kelvin is used extensively in scientific measurements because it allows for precise calculations and descriptions of thermodynamic processes, especially in physics and chemistry.

Common Benchmarks: Some common reference temperatures in the Kelvin scale include:

  • Boiling point of water: approximately 373.15 K at standard atmospheric pressure.
  • Freezing point of water: 273.15 K.
  • Room temperature: approximately 293 K to 298 K.

Relative Comparison to Other Scales: Kelvin directly relates to the Celsius scale by a simple addition or subtraction of 273.15, making it easy to convert between the two. Unlike Fahrenheit, which requires a more complex conversion formula, Kelvin and Celsius share the same incremental scale, differing only in their starting point (zero value).

The Kelvin scale is critical for scientific experiments and calculations, as it provides a thermodynamically absolute frame of reference that simplifies many formulae and theoretical models.

Effects of Kelvin

Scientific Research and Experimentation

  • Precision in Measurements: The Kelvin scale allows for precise and absolute measurements of temperature, which are crucial in fields like physics, chemistry, and engineering.
  • Thermodynamic Calculations: Kelvin is essential for calculations involving the laws of thermodynamics, as it starts at absolute zero, simplifying many thermodynamic equations by eliminating negative temperature values.

Standardization Across Disciplines

  • Universal Scientific Standard: Kelvin provides a consistent temperature measurement across all scientific disciplines, facilitating clearer communication and data comparison.
  • International Standards: The Kelvin scale is part of the International System of Units (SI), making it the standard unit of thermodynamic temperature measurement worldwide.

Technological and Industrial Applications

  • Material Science: Understanding how materials behave at various temperatures, especially near absolute zero, is crucial for developing superconductors and other advanced materials.
  • Cryogenics: Kelvin is the standard unit in cryogenics where extremely low temperatures are necessary, for example, in the storage of biological materials or in superconducting magnet applications.

Astrophysical Studies

  • Stellar Temperatures: The temperatures of stars and other celestial bodies are measured in Kelvin, which helps astronomers in classifying stars and understanding stellar evolution.
  • Cosmology: Kelvin is used to measure the Cosmic Microwave Background radiation, providing evidence of the Big Bang and aiding in the understanding of the universe’s origins and its temperature over time.

Educational Implications

Learning and Teaching: The introduction of Kelvin in education facilitates the understanding of absolute temperatures and basic physical concepts, such as entropy and the zeroth law of thermodynamics.


What is the triple point of water and why is it important to the Kelvin scale?

The triple point of water is the temperature and pressure at which water can coexist in three states: solid, liquid, and gas. It is precisely defined as 273.16 K. This point is used to calibrate temperature measurements and define the Kelvin scale with high precision.

Why does the Kelvin scale not use degrees like Celsius or Fahrenheit?

Kelvin is used as an absolute scale for scientific accuracy, so it measures temperature in Kelvins, not degrees. This emphasizes that the scale starts from an absolute zero, which is different from relative temperature scales like Celsius and Fahrenheit.

What is the significance of absolute zero on the Kelvin scale?

Absolute zero (0 K) is the theoretical lowest possible temperature, where all thermal motion ceases. This concept is crucial for understanding the fundamental principles of thermodynamics and quantum mechanics.

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