The SI unit of temperature is :

kelvin is the si unit of temperature

The kelvin (symbol: K) is the SI unit of temperature, used to measure the thermal state or heat of a substance. Unlike Celsius or Fahrenheit, which are based on arbitrary reference points, the kelvin scale starts at absolute zero (0 K), which represents the lowest possible temperature where all molecular motion ceases. 

This makes the kelvin scale an absolute temperature scale. Each degree on the kelvin scale is equivalent to one degree Celsius, but there is no negative kelvin value. The kelvin scale is crucial in scientific fields like thermodynamics, where precise and absolute temperature measurements are essential. By using kelvins, scientists can more accurately describe the energy contained within substances and understand temperature-related phenomena on a universal scale.