Convert Celsius to kelvin (°C to K)
To convert Celsius to kelvin, add 273.15 to the Celsius temperature. Students and scientists use it in gas-law and thermodynamics problems, and lighting buyers meet kelvin on bulb packaging. This celsius to kelvin converter works both ways: type Celsius or kelvin into either box above and the other box, the worked formula and the chart below update as you type.
The degree Celsius (°C) is named after the Swedish astronomer Anders Celsius, who proposed a 100-degree scale in 1742. Water freezes at 0 °C and boils at about 100 °C at sea level, and the scale is now formally defined from the kelvin. Celsius is the everyday scale for weather, cooking and medicine in nearly every country. A Celsius degree is exactly the same size as a kelvin, and 0 °C is 273.15 K.
The kelvin (K) is the SI base unit of temperature, named after Lord Kelvin (William Thomson). Its zero is absolute zero, the coldest temperature possible, and one kelvin is the same size as one degree Celsius. Zero kelvin is absolute zero, which is −273.15 °C. Kelvin is used in physics, chemistry, astronomy and cryogenics, and on light-bulb packaging to describe colour temperature — about 2,700 K for warm white and 6,500 K for daylight.
How to convert celsius to kelvin with this tool
- Type a number into the Celsius (°C) box — it starts at 25 °C as an example.
- Read the answer in the Kelvin (K) box and in the result panel, which also shows the formula with your number.
- To go the other way, type into the kelvin box, or press the swap button to open the Kelvin to Celsius converter with your value carried over.
- Choose how many decimal places you want, or tap a quick value such as −273.15 °C, −196 °C, 0 °C.
- Press Copy result to paste the conversion into a message, spreadsheet or note.
Celsius to Kelvin converter features
Converts both ways
Type in the Celsius box to get kelvin, or in the kelvin box to get Celsius. The other box follows instantly.
Exact factor
Calculations use K = °C + 273.15, and rounding is applied only to the answer you see — choose Auto or 0–10 decimal places.
Formula with your number
The working is shown under the result, for example 25 + 273.15 = 298.15 K, so you can check it or copy the method.
Quick values and chart
Tap common values like −273.15 °C, −196 °C, 0 °C, or read the Celsius-to-kelvin table further down this page.
Celsius to Kelvin formula
The formula is K = °C + 273.15. It is exact because the Celsius scale is defined as the kelvin scale shifted by exactly 273.15.
The reverse formula is °C = K − 273.15 — or use the Kelvin to Celsius converter. Three worked examples:
- Standard lab temperature (25 °C): 25 + 273.15 = 298.15 K
- Boiling water at sea level: 100 + 273.15 = 373.15 K
- Liquid nitrogen (about −196 °C): −196 + 273.15 = 77.15 K
Why science uses kelvin
Gas laws, thermodynamics and radiation formulas need absolute temperature, so values must be in kelvin before you multiply or divide them. Going from 20 °C to 40 °C is not “twice as hot”: in kelvin it is 20 °C = 293.15 K rising to 40 °C = 313.15 K, an increase of only about 7%.
Kelvin also describes the colour of light: a 2,700 K bulb gives a warm, yellowish light, while 5,000–6,500 K looks like daylight. Those numbers are colour temperatures, not how hot the bulb gets.
Celsius to Kelvin quick reference
The values people look up most often, worked out with the exact factor:
- −273.15 °C = 0 K
- −196 °C = 77.15 K
- 0 °C = 273.15 K
- 20 °C = 293.15 K
Quick tip: Just add 273.15 — or 273 for most homework. A change of 1 °C is exactly a change of 1 K, so temperature differences are identical on both scales.
Related conversions: Celsius to Fahrenheit, Fahrenheit to Kelvin and the full temperature converter.
Celsius to Kelvin conversion table
Values in kelvin are rounded to 2 decimal places (more for very small numbers). For any value not listed, type it into the converter above.
| °C | K | °C | K |
|---|---|---|---|
| −273.15 | 0 | 37 | 310.15 |
| −196 | 77.15 | 40 | 313.15 |
| −100 | 173.15 | 50 | 323.15 |
| −80 | 193.15 | 60 | 333.15 |
| −40 | 233.15 | 80 | 353.15 |
| −20 | 253.15 | 100 | 373.15 |
| −10 | 263.15 | 150 | 423.15 |
| 0 | 273.15 | 200 | 473.15 |
| 10 | 283.15 | 300 | 573.15 |
| 15 | 288.15 | 500 | 773.15 |
| 20 | 293.15 | 1,000 | 1,273.15 |
| 25 | 298.15 | 1,500 | 1,773.15 |
| 30 | 303.15 | 5,000 | 5,273.15 |
Celsius to Kelvin FAQ
What is 37 °C in kelvin?
37 degrees Celsius is 310.15 kelvin: 37 + 273.15 = 310.15 K.
How do I convert celsius to kelvin?
Add 273.15 to the Celsius temperature. For example, 20 + 273.15 = 293.15 K. To convert back, subtract 273.15 from the kelvin value — or use the Kelvin to Celsius converter.
What is 0 K in Celsius?
0 kelvin is −273.15 degrees Celsius, because 0 − 273.15 = −273.15 °C.
What does 20 °C equal in kelvin?
Why is there no degree sign in kelvin?
Since 1967 the unit has been called simply “kelvin” (K), not “degrees Kelvin”, because it is an absolute scale that starts at absolute zero. So you write 20 °C = 293.15 K, not 293.15 °K.