Calculate Kelvin from Celsius instantly by adding 273.15, and convert Kelvin back to Celsius in one tool.
Celsius to Kelvin Formula
To convert a temperature from Celsius to Kelvin, you add 273.15 to the Celsius value:
K = C + 273.15
To go the other way, from Kelvin back to Celsius, you subtract 273.15:
C = K - 273.15
Where:
- K is the temperature in kelvin
- C is the temperature in degrees Celsius
- 273.15 is the offset between the two scales, equal to the Celsius value of absolute zero
The Celsius and Kelvin scales use the same size degree, so a change of 1 degree Celsius is exactly a change of 1 kelvin. The only difference is where each scale starts. Celsius is set to 0 at the freezing point of water, while Kelvin starts at absolute zero, the lowest temperature possible. Because the step size is identical, converting between them only requires shifting by the fixed 273.15 offset rather than scaling. The calculator applies that shift in either direction and also reports the matching Fahrenheit value for reference.
Temperature Reference Points
These common points show how the two scales line up. Note that kelvin values are not written with a degree symbol.
| Reference point | Celsius | Kelvin |
|---|---|---|
| Absolute zero | -273.15 C | 0 K |
| Freezing point of water | 0 C | 273.15 K |
| Room temperature | 25 C | 298.15 K |
| Human body temperature | 37 C | 310.15 K |
| Boiling point of water | 100 C | 373.15 K |
Example Problems
Example 1. Convert 30 degrees Celsius to Kelvin.
Start with the formula K = C + 273.15. Substitute the Celsius value: K = 30 + 273.15. The result is 303.15 K.
Example 2. Convert 250 Kelvin to Celsius.
Use the reverse formula C = K - 273.15. Substitute the Kelvin value: C = 250 - 273.15. The result is -23.15 degrees Celsius.
FAQ
Why do you add 273.15 instead of 273?
The exact offset is 273.15 because absolute zero sits at -273.15 degrees Celsius. Many textbooks round to 273 for quick mental math, but using 273.15 gives the precise answer. The calculator always uses 273.15.
Can a Kelvin temperature be negative?
No. Kelvin starts at absolute zero, which is the coldest temperature possible, so it never goes below 0. If a Celsius value below -273.15 is entered, it would produce a negative Kelvin reading, which is not physically valid.
Do you write a degree symbol with Kelvin?
No. Celsius and Fahrenheit use the degree symbol, but kelvin is written as a plain number followed by K, for example 300 K rather than 300 degrees K.
