Celsius to Kelvin (°C to K)

How to convert Celsius to kelvin

Add 273.15:

K = °C + 273.15

25 °C + 273.15 = 298.15 K. A kelvin is the same size as a Celsius degree, so the scales differ only by where they start: Celsius puts zero at the freezing point of water, kelvin at absolute zero. Negative Celsius values work the same way — −196 °C + 273.15 = 77.15 K, close to the boiling point of liquid nitrogen. The result shows the addition with your number on the “worked out” line. To go back, subtract 273.15, or type the kelvins into the second field.

273 or 273.15?

The offset is exactly 273.15. Textbooks sometimes round it to 273, and that is fine when your data limit the precision anyway:

• 25 °C has no decimals, so 25 + 273 = 298 K keeps three significant figures — the same as 298.15 rounded.
• 25.0 °C or 25.00 °C carries more precision; use 273.15 and report 298.2 K or 298.15 K.
• For temperature differences the offset cancels: a rise of 10 °C is a rise of 10 K.
• Ratios need kelvins: going from 10 °C to 20 °C does not double the volume of a gas, because 283.15 K to 293.15 K is only a 3.5% rise.

If an answer key differs from yours in the last digit, check which offset it used. Use Decimal places to round the result to match.

Celsius to kelvin chart

For a lab table, open Convert a list of values, paste the Celsius readings one per line and download the CSV.

Reference temperatures

Light bulbs are rated in kelvins too: a “2700 K” warm white bulb describes the color of a body glowing at 2,700 K (about 2,427 °C), not the bulb’s actual temperature.

Writing kelvin correctly

Write 300 K, with a space and no degree sign; the unit is “kelvin” in lowercase, plural “kelvins”. The degree sign belongs to Celsius and Fahrenheit only. For everyday temperatures, see Celsius to Fahrenheit and Fahrenheit to Celsius; for lab volumes, mL to liters.