Kelvin (K) - Unit Information & Conversion

Definition

Kelvin (symbol: K) is the base unit of thermodynamic temperature in the International System of Units (SI). It is an absolute temperature scale, meaning 0 K represents absolute zero, the theoretical lowest possible temperature where all thermal motion ceases. Unlike Celsius and Fahrenheit, Kelvin is not expressed in degrees.

History

The Kelvin scale was proposed by William Thomson, 1st Baron Kelvin, in 1848. He recognized the need for an absolute thermodynamic scale based on the principles of thermodynamics, independent of the properties of any specific substance. Absolute zero (0 K) was determined by extrapolating the behavior of ideal gases. The size of one kelvin unit is defined as the same magnitude as one degree Celsius (1 K = 1°C in terms of temperature difference).

Common Uses

• Scientific Research: Scientific research, particularly in physics, chemistry, and thermodynamics.
• Cryogenics: Measurement of very low temperatures (cryogenics).
• Lighting & Photography: Color temperature measurement in lighting and photography.
• Astronomy: Astronomy and astrophysics for measuring celestial body temperatures.
• SI Standard: Official SI unit for temperature in scientific contexts.

Unit FAQs

Why doesn't Kelvin use degrees?

Kelvin represents an absolute scale starting from zero. The term 'degree' is typically associated with scales that have arbitrary reference points (like the freezing point of water). Since Kelvin starts at the fundamental limit of temperature, the unit itself is simply 'kelvin'.

What is absolute zero?

Absolute zero (0 K, or -273.15 °C, or -459.67 °F) is the lowest theoretical temperature. At this point, particles have minimal vibrational motion, retaining only quantum mechanical zero-point energy.

How does Kelvin relate to Celsius?

The conversion is straightforward because the size of the units is the same: K = °C + 273.15. To convert Kelvin to Celsius: °C = K - 273.15. A change of 1 K is identical to a change of 1°C.