What is K in Celsius?

If the K in the question refer to Kelvin, it is not "in Celsius".

The Celsius scale is an interval scale. This means that the difference between 5 deg C and 10 deg C is the same as that between 32 deg C and 37 deg C, or -56 deg C and -51 deg C. However, the choice of the 0 for this scale (the triple point of water) is arbitrary. As a result, 10 deg C is not twice anything that is 5 deg C (other its numerical value).

By contrast absolute temperature, measured in terms of thermodynamic activity, is measured in Kelvin. The difference between 5 Kelvin and 10 K is the same as the difference between 5 deg C and 10 deg C, or 32 deg C and 37 deg C. But additionally, 10 K represents double the thermodynamic activity than does 5 K.

So a Kelvin degree is the same change as a Celsius degree but 1 K = -272.15 deg C.