Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Convert Celsius to Kelvin instantly with the exact formula: K = °C + 273.15.
This tool shifts a Celsius reading onto the Kelvin (K) scale used throughout scientific work. It's the simplest of the temperature conversions -- a pure offset with no multiplication needed -- since Celsius and Kelvin use the same size "degree," just a different zero point.
Enter a Celsius temperature. The result updates instantly, showing the equivalent in Kelvin and Fahrenheit at the same time.
K = °C + 273.15
Celsius and Kelvin use identically sized degree increments -- a 1-degree change is the same in both scales -- so no multiplication is needed, only a fixed offset of 273.15, the exact gap between water's freezing point (0°C) and absolute zero (0 K).
| Celsius | Kelvin |
|---|---|
| -273.15°C (absolute zero) | 0.00 K |
| 0°C (freezing) | 273.15 K |
| 20°C (room temp) | 293.15 K |
| 37°C (body temp) | 310.15 K |
| 100°C (boiling) | 373.15 K |
Chemistry and physics coursework that requires an absolute temperature scale for formulas like the ideal gas law. Weather data analysis and scientific instrumentation that reports in Kelvin. For a US-Fahrenheit starting point instead, see the Fahrenheit to Kelvin Converter; for everyday Fahrenheit conversion, see the Celsius to Fahrenheit Converter.
Imagine a chemistry exercise that says a gas sample is held at 15°C and asks you to use the ideal gas law. The formula requires Kelvin, so add 273.15 to get 288.15 K. Only after that step can you plug the temperature into the equation. Forgetting the conversion and using 15 directly is one of the most common errors in introductory physical science, and it changes the answer dramatically.
15 + 273.15 = 288.15 K
The same rule works at both ends. For −40°C the result is 233.15 K. For 500°C, such as a furnace setting, the result is 773.15 K. In each case only the offset changes; the size of one degree is identical on both scales, so a rise of 20 degrees Celsius is also a rise of 20 kelvins.
This is the point that trips people up. If a sample warms from 20°C to 35°C, the temperature change is 15 in either unit. You only add 273.15 when you are converting an absolute reading, not when you are describing how much something changed. Formulas that involve heat, such as specific heat calculations, use temperature change, so the offset cancels out and you can use Celsius differences directly.
Use K without a degree symbol, as in 288.15 K. Keep the number of decimal places consistent with your measurement. If the temperature was measured to the nearest whole degree, many instructors accept rounding to 288 K, but follow your own course or lab instructions on significant figures instead of assuming.
Kelvin also appears in photography and lighting, where colour temperature is expressed in kelvins, though that is a description of light colour rather than a conversion from air temperature, so do not apply this converter to those values.
Add 273.15 to the Celsius value: K = °C + 273.15. No multiplication is needed -- it's a pure offset.
0°C (the freezing point of water) equals 273.15 K.
Kelvin is an absolute scale with no negative values, which makes it easier to use in physical formulas (like the ideal gas law) that require temperature to be proportional to energy.
It's defined by the precise gap between absolute zero and water's freezing point under standard conditions -- a fixed physical constant, not a rounded convenience figure.
Yes -- the 273.15 offset is an exact, internationally defined constant, not an approximation.
500 + 273.15 equals 773.15 K.
No. Differences are the same number in Celsius and Kelvin, so only absolute readings need the offset.
For rough classroom work many people use 273, but 273.15 is the exact value and is safer when you need precision. Follow your instructor's convention.
No. A negative result means the Celsius input was below absolute zero, which cannot occur physically, so the input should be checked.
The conversion formula is K = °C + 273.15. Here are common reference temperatures converted from Celsius (°C) to Kelvin (K).
| Celsius (°C) | Kelvin (K) |
|---|---|
| -40 | 233.15 |
| -18 | 255.15 |
| 0 | 273.15 |
| 10 | 283.15 |
| 20 | 293.15 |
| 25 | 298.15 |
| 37 | 310.15 |
| 60 | 333.15 |
| 100 | 373.15 |
| 180 | 453.15 |
Reference: NIST Weights and Measures