Celsius to KelvinFree online conversion calculator — instant results, no sign-up
Convert Celsius to Kelvin and back.
About the Celsius to Kelvin
The Celsius to Kelvin calculator converts a temperature in degrees Celsius to its equivalent on the Kelvin scale. It uses the exact offset of 273.15 between the two scales, so the default input of 25 °C gives 298.15 K. The reverse conversion subtracts the same offset from a Kelvin temperature.
- Temperature (°C)
- The temperature to convert, measured in degrees Celsius (°C), with a default value of 25.
Formula and method
K = °C + 273.15; reverse conversion: °C = K − 273.15.
- KThe numerical temperature value in kelvins.
- °CThe numerical temperature value in degrees Celsius.
- 273.15The exact offset between the Celsius and Kelvin temperature scales.
Add 273.15 to the Celsius input without applying any scaling factor, because a change of one degree Celsius equals a change of one kelvin. For the default input, K = 25 + 273.15 = 298.15 K. To convert back, subtract 273.15 from the Kelvin value: 298.15 − 273.15 = 25 °C.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Temperature25 °C
Results
- Kelvin298.15 K
- FormulaK = °C + 273.15
How to use the Celsius to Kelvin
- 1Enter the temperature in the Temperature (°C) field, or leave the default value of 25.
- 2Use the Celsius-to-Kelvin calculation to add 273.15 to the entered value.
- 3Read the Kelvin output; the default input produces 298.15 K.
- 4Check the Formula row, which shows K = °C + 273.15.
- 5For a reverse conversion, subtract 273.15 from the Kelvin value to recover the Celsius temperature.
Reading your result
The Kelvin row gives the converted absolute temperature: 298.15 K for the default input of 25 °C. Kelvin uses the symbol K without a degree sign. The Formula row shows K = °C + 273.15, identifying the rule used rather than a separate numerical result.
Limitations
This conversion is for temperature values, not temperature differences; differences have the same numerical size in Celsius and kelvins and do not require the offset. For ordinary physical temperatures, Celsius values below −273.15 °C would produce values below absolute zero and are not physically valid. The offset is exact, but conversion does not improve the precision or accuracy of the original measurement. The listed input is Celsius; the reverse formula is provided without assuming a separate Kelvin input or mode.
Common questions
Why does 25 °C convert to 298.15 K?+
The Kelvin scale starts 273.15 degrees below the Celsius zero point, so adding 273.15 to 25 gives 298.15 K.
How do I convert the Kelvin result back to Celsius?+
Subtract 273.15 from the Kelvin value. For the default result, 298.15 − 273.15 = 25 °C.
Should the Kelvin result include a degree sign?+
No. The correct notation for the default result is 298.15 K, not 298.15 °K.
Do I add 273.15 when converting a Celsius temperature change?+
No. Celsius and Kelvin have equal-sized intervals, so a temperature change has the same numerical value in both units. Add 273.15 only when converting a temperature value.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.