Celsius to Kelvin Converter
Type a temperature in Celsius to get kelvin, the SI unit used in physics and chemistry.
20 °C =
293.15K
20 degrees Celsius is 293.15 kelvins.
- In Fahrenheit
- 68 °F
How this works: Method, 3 sources, Checked against 1 worked example,
How this works
Method
Add 273.15 to the Celsius temperature. The kelvin and the degree Celsius are the same size; the scales differ only in where zero sits. Kelvin starts at absolute zero, the point where no more thermal energy can be removed, which is −273.15 °C. Full method
Sources
How it’s tested
One worked example for this page is checked by automated tests before every release: given the inputs, the tool must show the expected answer.
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Changes
- Ask understands “5 ft 9 in to cm” and “2 cups of flour in grams” and answers at once, and a decimal comma (“2,5”) reads as 2.5.
- First published: 89 everyday units across ten quantities, with 58 pages for common pairs such as cm to inches and Celsius to Fahrenheit.
How to convert Celsius to kelvin
Add 273.15 to the Celsius temperature. The kelvin and the degree Celsius are the same size; the scales differ only in where zero sits. Kelvin starts at absolute zero, the point where no more thermal energy can be removed, which is −273.15 °C.
A freezer at −10 °C is −10 + 273.15 = 263.15 K. Liquid nitrogen boils at about −195.8 °C, which is 77.35 K. Because the step is the same size, a change of 15 °C is also a change of 15 K.
Kelvin has no negative values, so a Celsius number below −273.15 has no answer: the converter flags it as below absolute zero.
K = °C + 273.15
- The SI defines the kelvin through the Boltzmann constant, k = 1.380649 × 10⁻²³ J/K exactly, and Celsius temperature as t = T − 273.15 K. The unit is written K, with no degree sign. Source: BIPM, The International System of Units (SI Brochure, 9th edition).
How to estimate Celsius to kelvin in your head
Add 273 and you will be within 0.15 K, which is closer than most thermometers read. For room temperature, 20 °C plus 273 gives 293 K; the exact figure is 293.15.
Chemists often round further: 0 °C ≈ 273 K and 25 °C ≈ 298 K are the standard reference temperatures you will see in data tables.
Celsius to kelvin table
Physics and chemistry reference points, from absolute zero to molten iron.
| Degrees Celsius (°C) | Kelvins (K) | Reference point |
|---|---|---|
| -273.15 | 0 | absolute zero |
| -195.8 | 77.35 | liquid nitrogen boils |
| -78.5 | 194.65 | dry ice sublimes |
| -40 | 233.15 | |
| -10 | 263.15 | |
| 0 | 273.15 | water freezes |
| 0.01 | 273.16 | triple point of water |
| 20 | 293.15 | |
| 25 | 298.15 | standard lab temperature |
| 37 | 310.15 |
Show all 13 rowsShow fewer
| 100 | 373.15 | water boils (1 atm) |
| 327.5 | 600.65 | lead melts |
| 1,538 | 1,811.15 | iron melts |
Frequently Asked Questions
Why is it “kelvin” and not “degrees kelvin”?
Since 1967 the unit has been named the kelvin, symbol K, as an absolute scale with no degree sign. So write 300 K, read as “300 kelvins”, not °K.
Is it 273 or 273.15?
273.15 is the exact offset by definition. Many school textbooks use 273, which is fine when your measurements are only good to the nearest degree.
What is 20 °C in kelvin?
20 °C is 293.15 K. Room-temperature gas law problems often use this value, or 298.15 K for 25 °C.