Kelvin to Celsius
Convert kelvin to Celsius — type a temperature in either box. The formula is °C = K − 273.15.
How to use
- Enter a temperature in the Kelvin field.
- The Celsius value updates instantly.
- Negative values work exactly the same way.
- Check the reference table for the fixed points.
Kelvin to Celsius formula
Temperature is the one conversion that needs more than a multiplication: the scales disagree about where zero sits, so an offset is required as well as a ratio.
°C = K − 273.15
Apply the offset first, then the ratio — reversing the order is the most common mistake.
Worked example
Converting 37 K gives -236.15 °C.
37 K → -236.15 °C
Reference points
Four temperatures worth memorizing, in both scales:
| Reference point | Kelvin | Celsius |
|---|---|---|
| water freezing | 273.15 K | 0 °C |
| a mild room | 293.15 K | 20 °C |
| body temperature | 310.15 K | 37 °C |
| water boiling | 373.15 K | 100 °C |
What is a kelvin?
The kelvin is the SI base unit of thermodynamic temperature, counting from absolute zero rather than from a property of water.
Definition: Since 2019 defined by fixing the Boltzmann constant at exactly 1.380649×10⁻²³ joules per kelvin. Absolute zero is 0 K, which is −273.15 °C.
Where it is used: Physics and chemistry, color temperature of lighting, and astronomy.
Worth knowing: Written 'kelvin', not 'degrees kelvin', and the symbol K takes no degree sign.
What is a degree Celsius?
Celsius is the everyday temperature scale in nearly every country, with 0 °C at water's freezing point and 100 °C at its boiling point.
Definition: Now defined from the kelvin: a temperature in °C equals the kelvin value minus exactly 273.15. Since 2019 the kelvin itself is fixed by the Boltzmann constant.
Where it is used: Weather forecasts, cooking, medicine and science worldwide outside the United States.
Worth knowing: A degree Celsius and a kelvin are the same size, so a temperature difference is numerically identical in both — only absolute readings differ.
Frequently asked questions
What is the formula to convert kelvin to Celsius?
Use °C = K − 273.15.
What is 0 K in Celsius?
0 K is -273.15 °C.
What is 100 K in Celsius?
100 K is -173.15 °C.
Does this work for negative temperatures?
Yes. The formula is linear, so it is valid above and below zero on either scale.
Is there anything to watch out for with kelvin?
Written 'kelvin', not 'degrees kelvin', and the symbol K takes no degree sign.
Is there anything to watch out for with celsius?
A degree Celsius and a kelvin are the same size, so a temperature difference is numerically identical in both — only absolute readings differ.