About the Celsius to Kelvin
This Celsius to Kelvin converter changes a temperature in degrees Celsius into kelvin, the SI base unit of temperature used in physics, chemistry and engineering. It also converts in the other direction — type a kelvin value in the second field to get degrees Celsius and Fahrenheit — so you can check lab data, gas-law problems or color-temperature figures without juggling formulas.
Students working through ideal gas law or thermodynamics questions need absolute temperatures, and so do engineers reading sensor data or photographers comparing light color temperatures quoted in kelvin. The reference table lists landmark temperatures from absolute zero to the surface of the Sun.
The conversion is exact by definition: a kelvin is the same size as a degree Celsius, and 0 °C is exactly 273.15 K. Kelvin never goes negative, so any Celsius value below −273.15 °C is flagged as physically impossible.
With the default inputs, the kelvin is 298.15 K. Change any value above to recalculate instantly.
How to use the celsius to kelvin
- 1Enter the temperature in degrees Celsius.
- 2Read the kelvin result, plus Fahrenheit and Rankine equivalents.
- 3To convert kelvin to Celsius, type the kelvin value in the second field.
- 4Check the working line or the reference table for common temperatures.
Formula and method
Kelvin and Celsius use degrees of exactly the same size; they only differ in where zero sits. Kelvin starts at absolute zero, the lowest possible temperature, which is −273.15 °C. So you add 273.15 to a Celsius reading to get kelvin, and subtract 273.15 from kelvin to get Celsius.
Because the step size is identical, a change of 10 °C is also a change of 10 K. Kelvin is written without a degree sign ("300 K", not "300 °K"). Rankine is the Fahrenheit-sized absolute scale: °R = K × 1.8.
- K
- Temperature in kelvin (absolute, never negative)
- °C
- Temperature in degrees Celsius
- °R
- Temperature in degrees Rankine (K × 1.8)
Worked examples
Standard lab temperature: 25 °C
25 + 273.15 = 298.15 K, the "standard temperature" used in chemistry tables. In reverse, 300 K − 273.15 = 26.85 °C, or 80.33 °F.
Boiling water: 100 °C
100 + 273.15 = 373.15 K. Entering 0 K in the reverse field gives −273.15 °C — absolute zero, the bottom of the scale.
Body temperature and the Sun
Normal body temperature of 37 °C is 310.15 K. The Sun’s surface is often quoted as 5,778 K, which is 5,778 − 273.15 = 5,504.85 °C or about 9,941 °F.
Frequently asked questions
What is the formula to convert Celsius to Kelvin?+
Add 273.15 to the Celsius temperature: K = °C + 273.15. For example, 20 °C + 273.15 = 293.15 K. To go back, subtract 273.15.
Why is it 273.15 and not 273?+
Absolute zero is −273.15 °C by definition in the SI system. Many textbooks round to 273 for quick work, which introduces an error of 0.15 K — fine for rough answers, not for precise lab data.
Can kelvin be negative?+
No. Zero kelvin is absolute zero, the point where particles have minimal thermal energy, so the kelvin scale has no negative values. A negative kelvin result means an input error.
Why don't we say "degrees kelvin"?+
Since 1967 the unit has been simply the "kelvin" (symbol K) with no degree sign, because it is an absolute SI base unit rather than a scale relative to a reference point like water.
Is a change of 1 °C the same as 1 K?+
Yes. The degree Celsius and the kelvin are the same size, so a temperature difference of 15 °C is exactly 15 K. Only the zero point differs.