Convert CELSIUS to KELVIN, Free
Type any CELSIUS value and see the KELVIN result instantly. No button press needed.
How to convert CELSIUS to KELVIN
Kelvin is the SI base unit of thermodynamic temperature and starts at absolute zero, the point at which molecular motion theoretically stops. Converting from Celsius to Kelvin is straightforward: add 273.15 to the Celsius value. This conversion is essential in chemistry, physics, and engineering because many physical laws (the ideal gas law, Planck's radiation formula, entropy calculations) require temperature in Kelvin to work correctly.
Unlike the Celsius-to-Fahrenheit conversion that requires both multiplication and addition, Celsius and Kelvin use the same scale interval: a change of 1 degree Celsius is identical to a change of 1 Kelvin. Only the zero point differs, offset by exactly 273.15.
Enter the Celsius temperature
Type your Celsius value in the input field. Negative values are valid and common for sub-zero temperatures.
Read the Kelvin result
The converter adds 273.15 to your input and displays the Kelvin equivalent immediately.
Use in calculations
Copy the Kelvin value for use in ideal gas law problems (PV = nRT), Stefan-Boltzmann calculations, or any formula requiring absolute temperature.
Convert back if needed
To reverse the conversion, subtract 273.15 from the Kelvin value, or use the Kelvin to Celsius converter.
Frequently asked questions
What is the formula to convert Celsius to Kelvin?
K = C + 273.15. The offset 273.15 is the freezing point of water in Kelvin. So 0 degrees Celsius = 273.15 K, and 100 degrees Celsius = 373.15 K.
Why do scientific equations use Kelvin instead of Celsius?
Equations like PV = nRT (ideal gas law) require an absolute temperature scale where zero means zero molecular energy, not an arbitrary reference point like water's freezing point. Negative Kelvin values are physically impossible in classical thermodynamics, which makes Kelvin mathematically reliable in formulas.
What is absolute zero in Celsius?
Absolute zero is 0 K, which equals -273.15 degrees Celsius. At this temperature, a classical gas would have zero volume and pressure. In practice, quantum effects prevent reaching true absolute zero.
Is there a difference between using 273 and 273.15?
For most classroom problems, 273 is close enough. For scientific and engineering work, use 273.15, which is the precise value adopted by the International Bureau of Weights and Measures. The 0.15 difference matters in high-precision calculations.
Do Kelvin values use a degree symbol?
No. Kelvin is written as K (not degrees K). The degree symbol is reserved for Celsius and Fahrenheit. So you write 300 K, not 300 degrees K.