Celsius to Kelvin
This free Celsius to Kelvin converter adds the exact offset 273.15 to any Celsius value and shows the kelvin result on every keystroke.
How to use
- Type a temperature in degrees Celsius into the Value box.
- The equivalent in kelvin appears instantly as you type.
- Swap the From and To selects to convert kelvin back to Celsius.
- Copy the full equation shown under the result into your notes or document.
Frequently asked questions
What is the formula for Celsius to Kelvin?
K = °C + 273.15. For example, 100 °C + 273.15 = 373.15 K. It is a pure offset, not a multiplication, because the two scales share the same degree size and differ only in their zero points.
Why is 0 °C equal to 273.15 K and not 0 K?
The kelvin scale starts at absolute zero, the temperature at which particles have minimum thermal motion, which sits 273.15 degrees below the freezing point of water. So 0 K is −273.15 °C and water freezes at 273.15 K.
Can kelvin be negative?
Not for ordinary temperature. Since 0 K is absolute zero, no physical temperature is below it, which is exactly why physics and chemistry formulas are written in kelvin — no negative-temperature sign errors.
Is a kelvin the same size as a degree Celsius?
Yes — an interval of 1 K is exactly an interval of 1 °C, so temperature differences never need converting between the two. Only the starting point differs, by the fixed 273.15 offset.
Related tools
About this tool
This free Celsius to Kelvin converter adds the exact offset 273.15 to any Celsius value and shows the kelvin result on every keystroke. The kelvin is the SI base unit of temperature, and its scale has the same step size as Celsius — one kelvin is exactly one degree Celsius of interval — but its zero sits at absolute zero, the coldest possible temperature. That zero-point shift is why the formula is K = °C + 273.15 rather than any multiplication: 0 °C, water’s freezing point, is 273.15 K, and 100 °C, its boiling point at sea level, is 373.15 K. Because kelvin readings never go negative, gas-law and thermodynamics problems in homework and labs are always worked in kelvin, and this page converts the Celsius numbers from a recipe, a weather report or a lab notebook into that form instantly. The full equation prints under every result. Useful anchors: room temperature 25 °C is 298.15 K, and −273.15 °C is 0 K, absolute zero itself. Everything runs locally in your browser: the values you type are never uploaded, stored or logged. To convert the other way, swap the From and To selects and the page becomes kelvin to Celsius in one click.