Kelvin (K) is the primary unit of temperature measurement in the International System of Units (SI). It is named after the Scottish physicist William Thomson, 1st Baron Kelvin. The Kelvin scale is an absolute temperature scale where zero Kelvin, also known as absolute zero, is the point at which all molecular motion ceases.

The Kelvin scale is based on the concept of thermodynamic temperature, which is directly proportional to the average kinetic energy of the particles in a substance. Unlike the Celsius and Fahrenheit scales, which have arbitrary starting points, the Kelvin scale begins at absolute zero, which is the lowest possible temperature.

The Kelvin scale uses the same size of degree increment as the Celsius scale, where 1 Kelvin is equivalent to 1 degree Celsius. However, the zero point on the Kelvin scale (absolute zero) is set at -273.15 degrees Celsius.

The Kelvin scale is widely used in scientific research, particularly in fields such as physics, chemistry, and engineering. It is especially useful in calculations involving gases, thermodynamics, and absolute temperature measurements, as it directly corresponds to the energy and motion of particles. Unlike the Rankine scale, the Kelvin scale is internationally recognized and adopted as the standard unit of temperature measurement.