The Celsius to Kelvin formula
To convert Celsius to Kelvin, add 273.15: K = °C + 273.15. For example, 25 °C + 273.15 = 298.15 K. The two scales share the same degree size, so a change of 1 °C equals a change of 1 K. To go the other way, use the Kelvin to Celsius calculator.
Because the offset is a constant, differences carry across unchanged: a rise from 20 °C to 25 °C is a rise of 5 °C and also a rise of 5 K. This matters in physics and engineering, where temperature differences can be quoted in kelvin even when the readings themselves were taken in Celsius.
How to convert °C to K
Enter a temperature in Celsius and the calculator adds the offset 273.15 to give Kelvin. Kelvin is the SI base unit for temperature and is used in physics, chemistry, and engineering. Absolute zero is 0 K, which equals −273.15 °C.
The 273.15 offset is exact, not rounded, so keep the decimals when precision matters. Rounding to 273 shifts every answer by 0.15 K, which is harmless for a weather forecast but not for calibration work or gas-law calculations, where absolute temperature sits directly in the equation.
Kelvin is also required whenever a formula uses temperature as a ratio. Doubling the absolute temperature of a gas at constant pressure doubles its volume, but doubling 20 °C to 40 °C does nothing of the sort — in kelvin those are 293.15 K and 313.15 K, a rise of under 7%.
The celsius to fahrenheit calculator answers the question that usually follows this one.
Celsius to Kelvin reference table
| Celsius | Kelvin |
|---|---|
| −273.15 °C | 0 K |
| 0 °C | 273.15 K |
| 25 °C | 298.15 K |
| 100 °C | 373.15 K |
Many people follow this up with the fahrenheit to kelvin calculator.
Frequently asked questions
- What is 25 Celsius in Kelvin?
- 25 °C equals 298.15 K (25 + 273.15).
- What is the Celsius to Kelvin formula?
- K = °C + 273.15.
- Why is there no negative Kelvin?
- The Kelvin scale starts at absolute zero (0 K = −273.15 °C), the coldest possible temperature, so values cannot go below zero.
- How do I convert Kelvin back to Celsius?
- Subtract 273.15, or use the Kelvin to Celsius calculator.
- Should I write “degrees Kelvin” or just “Kelvin”?
- Just kelvin, and the symbol is a plain K with no degree sign — 298.15 K, never 298.15 °K. The kelvin is an SI base unit rather than a degree scale, which is why the symbol drops the degree symbol that Celsius and Fahrenheit keep.