How to Convert Celsius to Kelvin
To convert Celsius to Kelvin, add 273.15 to the Celsius value. The formula is K = °C + 273.15. That is the entire conversion — unlike Fahrenheit, the Kelvin and Celsius scales use degrees of the same size, so you only shift the starting point, you never multiply. The converter above does it instantly for any temperature.
The Celsius to Kelvin Formula
Kelvin is the SI base unit of temperature and starts at absolute zero, the coldest possible temperature, which is −273.15 °C. Because a one-degree change is identical on both scales, converting is just a matter of adding 273.15 to go from Celsius to Kelvin, or subtracting 273.15 to go from Kelvin back to Celsius. There are no negative Kelvin values, since nothing can be colder than absolute zero.
Worked Examples
0 °C (freezing point of water): 0 + 273.15 = 273.15 K. 25 °C (room temperature): 298.15 K. 100 °C (boiling point of water): 373.15 K. Body temperature of 37 °C is 310.15 K, and a cold −40 °C is 233.15 K.
Common Celsius to Kelvin Values
Quick reference: −273.15 °C = 0 K (absolute zero), 0 °C = 273.15 K, 20 °C = 293.15 K, 37 °C = 310.15 K, and 100 °C = 373.15 K. Because you always add the same 273.15, the gap between any Celsius and Kelvin reading is constant, which makes the scales easy to move between once you remember the offset.
Why Convert Celsius to Kelvin?
Kelvin is the standard unit in science — physics, chemistry, and engineering — because it starts at absolute zero, which makes the math of gas laws, thermodynamics, and many formulas far cleaner. Students and researchers convert Celsius to Kelvin constantly when solving problems that require an absolute temperature scale. Outside the lab, Celsius remains the everyday unit, so being able to add 273.15 quickly bridges classroom or technical work and real-world temperatures.
Kelvin, Celsius, and Absolute Zero
The key idea behind Kelvin is absolute zero: the point where molecular motion is at its minimum, defined as 0 K or −273.15 °C. By anchoring the scale there, Kelvin avoids negative numbers in scientific calculations and makes proportional relationships meaningful — doubling the Kelvin temperature of a gas, for example, has a clear physical meaning that doubling its Celsius value does not. This is why scientists adopted it as the base unit, even though daily life still runs on Celsius (or Fahrenheit). The converter above also handles Fahrenheit, so you can move among all three scales.
Frequently Asked Questions
What is the formula for Celsius to Kelvin?
K = °C + 273.15. Just add 273.15 to the Celsius temperature.
What is 25 °C in Kelvin?
25 °C is 298.15 K.
What is absolute zero in Celsius?
Absolute zero (0 K) is −273.15 °C.
Kelvin in Science
Kelvin is the temperature unit of science because it is an absolute scale, starting at absolute zero rather than an arbitrary point like the freezing of water. That property makes physical laws work cleanly. The ideal gas law, for instance, relates pressure and volume to absolute temperature — double the Kelvin temperature of a gas at constant pressure and its volume doubles, a relationship that simply does not hold with Celsius because Celsius can be negative and its zero is arbitrary. Thermodynamics, blackbody radiation, and reaction-rate calculations all rely on Kelvin for the same reason, which is why students convert Celsius to Kelvin before plugging values into these formulas.
Everyday Temperatures in Kelvin
It can help to picture familiar temperatures on the Kelvin scale. A comfortable room at 21 °C is about 294 K; a hot summer day of 35 °C is about 308 K; water freezes at 273.15 K and boils at 373.15 K; and a freezer at −18 °C sits around 255 K. Lighting uses Kelvin too — “warm white” bulbs are around 2,700 K and daylight is about 5,500 K — though that color-temperature scale is a related but separate use. For converting actual temperatures, the rule never changes: add 273.15 to Celsius for Kelvin, and the converter also handles Fahrenheit if you need all three scales.
More Free Online Tools
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