Why and how is 1 degree Celsius taken as 273.15 Kelvin?

The kelvin is a unit of measure for temperature based upon an absolute scale. It is one of the seven base units in the International System of Units (SI) and is assigned the unit symbol K. read more

Unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to or typeset as a degree. The kelvin is the primary unit of temperature measurement in the physical sciences, but is often used in conjunction with the Celsius degree, which has the same magnitude. read more

Now, if you want to know instead why a change of 1 degree celsius on the celsius scale (e.g., 24 degree celsius - 23 degree celsius = 1 degree celsius) corresponds to a change of the 1 kelvin on Kelvin scale (e.g., 297.15 kelvin - 296.15 kelvin = 1 kelvin) it’s simple: that is simple how the scale was chosen. read more

If one insists that one Kelvin degree is equally large as one Celsius degree as a unit of temperature difference, it just turns out that the melting point of ice has to be 273.15 K and the boiling point of water is 373.15 K. read more