How do you convert Celsius to kelvin?
Add 273.15. 0 °C is 273.15 K, 25 °C is 298.15 K and 100 °C is 373.15 K.
- 0 °C
- 273.15 K
- 0 K
- −273.15 °C
- Step of 1 °C
- Step of 1 K
Same size degrees, different zero
A change of one degree Celsius is a change of one kelvin, so temperature differences are identical on both scales. Only the starting point differs: kelvin counts from absolute zero, while Celsius puts 0 close to the freezing point of water.
Since 2019 the kelvin has been defined by fixing the Boltzmann constant at exactly 1.380649 × 10⁻²³ J/K, and the Celsius scale is defined from the kelvin by subtracting 273.15 (BIPM SI Brochure).
This is why scientific papers can report a temperature change in kelvins even when the readings were taken in Celsius.
- Absolute zero
- Also called 0 K · −273.15 °C
- The temperature at which a system has the least possible thermal energy. Nothing can be colder, so a kelvin value is never negative, and the converter flags any input below it.
Celsius to kelvin table
| Degrees Celsius (°C) | Kelvins (K) |
|---|---|
| -40 | 233.15 |
| -20 | 253.15 |
| -10 | 263.15 |
| 0 | 273.15 |
| 10 | 283.15 |
| 15 | 288.15 |
| 20 | 293.15 |
| 25 | 298.15 |
| Degrees Celsius (°C) | Kelvins (K) |
|---|---|
| 30 | 303.15 |
| 37 | 310.15 |
| 40 | 313.15 |
| 50 | 323.15 |
| 60 | 333.15 |
| 80 | 353.15 |
| 100 | 373.15 |
Writing kelvin correctly
Do
- Write 300 K, with a space and no degree sign.
- Use kelvin in gas laws and radiation formulas, which need absolute temperature.
Avoid
- Writing °K or degrees kelvin; the degree was dropped in 1967.
- Adding 273 instead of 273.15 in lab work, where the 0.15 matters.
Kelvin also turns up outside the lab: bulbs and camera white balance use color temperature, where 2700 K is warm white and 6500 K is close to daylight. For Fahrenheit, see celsius to fahrenheit or fahrenheit to kelvin.
Gas laws, heat radiation and electronic noise formulas all expect kelvin, so a Celsius reading should be converted before it goes into one of them.
Celsius to kelvin questions
What is 20 °C in kelvin?
20 + 273.15 = 293.15 K.
Can a temperature in kelvins go below zero?
No. 0 K is absolute zero, the lowest temperature possible, so every real temperature is zero kelvin or above.
Why is there no degree sign on K?
The unit was renamed from degree Kelvin to kelvin in 1967, and the degree sign was dropped with it. Write 300 K, not 300 °K.
What is a normal room temperature in kelvins?
Around 293 to 298 K, which is 20 to 25 °C.