How to Convert Celsius to Kelvin
Convert Celsius to Kelvin using the formula K = °C + 273.15, with a worked example, a quick reference chart, and the rule behind Kelvin's missing degree symbol.
Last updated: 2026-05-21
Converting Celsius to Kelvin is the simplest temperature conversion you will ever do. The two scales share the exact same step size — one degree Celsius is the same magnitude as one kelvin — so the only difference is where each scale places its zero point. That makes the conversion a single addition, with no multiplying or scaling required.
The formula is:
K = °C + 273.15
The constant 273.15 exists because the Kelvin scale starts at absolute zero — the coldest temperature physically possible — while Celsius starts at the freezing point of water. Absolute zero sits 273.15 degrees below that freezing point, so adding 273.15 shifts every Celsius reading onto the Kelvin scale.
Step by Step
Convert 25 °C to Kelvin:
- Start with your Celsius value: 25 °C.
- Add the constant 273.15 to it: 25 + 273.15.
- Read the result: 298.15 K.
That is the entire process — one addition. So 25 °C equals 298.15 K, which is a comfortable room temperature. To check any value instantly, use the temperature converter.
Celsius to Kelvin Chart
| Celsius | Kelvin | Reference point |
|---|---|---|
| −273.15 °C | 0 K | Absolute zero |
| 0 °C | 273.15 K | Freezing point of water |
| 25 °C | 298.15 K | Room temperature |
| 37 °C | 310.15 K | Human body temperature |
| 100 °C | 373.15 K | Boiling point of water |
Notice that the gap between any Celsius reading and its Kelvin value is always exactly 273.15. Because the scales move in lockstep, a change of 10 degrees Celsius is also a change of 10 kelvin — only the labels differ.
Why No Degree Symbol on Kelvin
Celsius and Fahrenheit are degree scales, so we write 25 °C or 77 °F. Kelvin is different. It is an SI base unit of temperature in its own right, like the meter or the kilogram, rather than a scale of degrees. For that reason a temperature is written as 300 K, never 300 °K, and you say "300 kelvin" instead of "300 degrees Kelvin."
The unit name is also lowercase — "kelvin" — even though it honors the physicist Lord Kelvin, while the symbol K is always capitalized. Getting this right signals technical precision, which matters in scientific and engineering writing.
Whenever you need to move between Celsius, Kelvin, Fahrenheit, or Rankine, the temperature converter handles every scale with full decimal precision so you never have to round by hand.