The absolute temperature scale based on absolute zero and using degree intervals equal in size to Celsius is the Kelvin scale. Its zero point is absolute zero, and a temperature change of 1 kelvin equals a change of 1 degree Celsius.
The kelvin is the SI base unit of thermodynamic temperature, written K rather than °K. Celsius and kelvin are related by T(K) = t(°C) + 273.15, so 0 °C corresponds to 273.15 K and −273.15 °C corresponds to 0 K.
William Thomson, later Lord Kelvin, proposed an absolute thermometric scale in 1848. Unlike scales anchored to convenient physical reference points such as water’s freezing point, an absolute scale reflects the lower limit imposed by thermodynamics.
A common mix-up is confusing kelvin with Rankine. Both begin at absolute zero, but Rankine uses Fahrenheit-sized degrees, while kelvin uses Celsius-sized intervals. The unit name is lowercase in scientific writing, although “Kelvin scale” is conventionally capitalized when referring to the scale or its namesake.