Celsius to Kelvin Converter (°C to K)

Kelvins start at absolute zero, so every physical law that depends on temperature in absolute terms, from the ideal gas law PV = nRT to radiation and reaction-rate equations, needs the reading in kelvins. Celsius converts by adding 273.15, the offset the SI fixes between the two scales; the size of one degree does not change.

This is the step students most often skip. Warming a gas from 10 °C to 20 °C does not double its pressure, because in kelvins the change runs only from 283.15 K to 293.15 K, an increase of about 3.5%. Chemistry tables usually quote data at 25 °C, written as 298.15 K, and cryogenic liquids are far easier to compare on the kelvin scale.

How to use this tool

1. Type a value in the Celsius box to see it in kelvins, or type in the Kelvin box to convert the other way.
2. Press ⇄ to swap the two units, or Load example for a typical value.
3. Check the charts below for common values; for other units, open the Temperature converter.

Formula

K = °C + 273.15

°C = K − 273.15

The scales have different zero points, so the formula adds or subtracts an offset as well as multiplying.

Example

Two conversions worked with the same factors the converter uses:

25 °C = 298.15 K

77 K = -196.15 °C

Celsius to Kelvin chart

Common values from degrees Celsius to kelvins, rounded to four decimal places.

Kelvin to Celsius chart

The reverse direction for values people often look up.

Lab and science reference points in Celsius

Quick mental estimate

Add 273 for a figure good to within 0.15 K: 25 °C → 298 K. For lab work keep the full 273.15, so 25 °C is 298.15 K; the difference only shows when results are reported to tenths or hundredths of a kelvin.

Use the converter or the charts when the exact figure matters.

The two units

Celsius (°C): Celsius temperature is the kelvin value minus exactly 273.15. At standard atmospheric pressure, pure water freezes near 0 °C and boils near 100 °C; these water temperatures are reference points, not the modern definition of the scale.

Kelvin (K): The kelvin is the SI base unit of thermodynamic temperature, defined since 2019 by fixing the Boltzmann constant at exactly 1.380649 × 10⁻²³ J/K. The scale starts at absolute zero (0 K), and 0 °C is exactly 273.15 K.