Example 1
- Value: 25 °C
- Direction: °C → K
298.15 K
A 25 °C room is 298.15 K, a common chemistry reference.
Kelvin to Celsius
Type a temperature and pick °C to K or K to °C. 25 °C is 298.15 K. The degree size is the same; only zero shifts. 0 K is absolute zero, −273.15 °C.
Absolute scale. Weather and oven: Celsius and Fahrenheit.
Result
Enter a temperature value.
How results are calculated
K = °C + 273.15. The other way: °C = K - 273.15. 0 °C is 273.15 K. A 25 °C room is 298.15 K. 20 °C is 293.15 K. 37 °C body temperature is 310.15 K. 100 °C boiling is 373.15 K. 0 K is -273.15 °C, absolute zero. -40 °C is 233.15 K, the same point as -40 °F on the Fahrenheit page.
Chemistry and physics write kelvin; weather writes °C. Type 25 and leave Celsius when that is room temperature in the lab. 373.15 K back is 100 °C. A 273 shortcut instead of 273.15 is fine for a rough estimate; the calculator adds 273.15.
Pick the direction from the list: °C to K or K to °C. A comma and a period both work. Typed 0 K is -273.15 °C. An empty field does not start a calculation. Two decimals are display only. The switch does not rewrite a typed number.
Convert Fahrenheit next door. Here it stays kelvin and Celsius, the absolute scale. Weather and oven do not need kelvin unless you describe a gas or a reaction.
A Celsius degree and a kelvin have the same size. Only the zero point differs. A negative kelvin does not exist in nature. The calculator still shows a number if you type a minus, but that is not a physical temperature.
Zero Celsius is freezing, 273.15 K, not zero kelvin. Zero kelvin is the bottom of the scale. Do not mix those two zeros in one field.
How to use
- Type a temperature number, for example 25 or 273.15.
- Pick °C to K or K to °C.
- Click Calculate. 25 °C gives 298.15 K. 0 °C gives 273.15 K.
- The shift is fixed: plus or minus 273.15. Zero kelvin is −273.15 °C.
- For weather, open Celsius and Fahrenheit. Here it stays kelvin.
K and °C, absolute zero
K = °C + 273.15. 25 °C is 298.15 K. 0 °C is 273.15 K. 0 K is −273.15 °C. The degree size is the same.
- K
- Temperature in kelvin. 298.15 at 25 °C. 0 K is absolute zero.
- °C
- The Celsius scale. 0 °C is ice, 100 °C is boiling. Shift +273.15 to get K.
Usage examples
Example 2
- Value: 0 K
- Direction: K → °C
−273.15 °C
0 K is absolute zero, -273.15 °C, the bottom of the scale.
Example 3
- Value: 37 °C
- Direction: °C → K
310.15 K
37 °C body temperature is 310.15 K in physiology notes.
Example 4
- Value: 100
- Direction: C
373.15 K
100 °C boiling is 373.15 K.
Example 5
- Value: -40
- Direction: C
233.15 K
-40 °C is 233.15 K. That is the same point as -40 °F on the Fahrenheit page.
Example 6
- Value: 373.15
- Direction: K
100 C
373.15 K back to Celsius is 100 °C.
Example 7
- Value: 20
- Direction: C
293.15 K
A 20 °C room is 293.15 K.
Example 8
- Direction: C
273.15 K
0 °C freezing is 273.15 K, not zero kelvin.
Related calculators
FAQ
How do I convert °C to kelvin?
Add 273.15: K = °C + 273.15. The other way you subtract: °C = K − 273.15. Same degree step.
How many kelvin is 0 °C and 25 °C?
0 °C is 273.15 K. 25 °C is 298.15 K. 20 °C is 293.15 K. Only the zero moves.
Can kelvin be negative?
Not in nature. 0 K is absolute zero. The calculator will compute a typed minus, but that is not a physical temperature.
Do a Celsius degree and a kelvin have the same size?
Yes. Only zero differs. A 1 K rise is a 1 °C rise. The scale does not squeeze or stretch.
Does an empty field count as 0 K?
No. An empty field does not start a calculation. Typed 0 on K to °C gives −273.15 °C, absolute zero.
How many K is boiling water and 37 °C body temperature?
Boiling 100 °C is 373.15 K. 37 °C is 310.15 K. Both from the same 273.15.
Where is Fahrenheit?
On the Celsius and Fahrenheit page. This calculator stays the absolute scale, with no °F field.
Is 273 enough instead of 273.15?
For a rough estimate, yes. The calculator adds 273.15. A 0.15 K miss at room temperature is already another hundredth.
Does a comma in 273.15 work?
Yes. 273.15 and 273,15 are the same zero shift. A comma and a period mean the same value.
How many K is -40 °C?
233.15 K. That is the same point as −40 °F on the Fahrenheit page; here you only compute K.
Knowledge sources
The scale in this calculator is the SI conversion. NIST SP 330 and BIPM define the kelvin; this is not a calibration certificate.
Page updated in 2026.