To calculate a temperature in Kelvin, add 273.15 to the Celsius temperature. Then round off your answer to the correct number of significant digits.
For example, what is -25 oC, in K?
K = oC + 273.15
K = -25 + 273.15 = 248.15
Rounded off, this is 248 K
Note: there is no degree symbol on Kelvin temperatures.