| Celsius (°C) | Kelvin (K) |
|---|
To convert Celsius to Kelvin, simply add 273.15. The Kelvin scale starts at absolute zero and uses the same interval size as Celsius:
Kelvin has no negative values — 0 K (absolute zero) is the lowest possible temperature, equal to −273.15°C.
Key temperature landmarks in Celsius and Kelvin:
To convert from Celsius to Kelvin, add 273.15 to the Celsius temperature. For example, 25°C = 25 + 273.15 = 298.15 K. To go the other way (Kelvin back to Celsius), subtract 273.15. The Kelvin scale and Celsius scale use the same interval size — a difference of 1°C is exactly a difference of 1 K.
The offset of 273.15 comes from the definition of absolute zero: the point at which all molecular motion theoretically ceases. Absolute zero is −273.15°C, so Kelvin starts there and counts up in the same unit steps as Celsius.
Kelvin is the SI base unit of temperature and is used in scientific and engineering contexts — thermodynamics, physics, chemistry, and astronomy. You'll encounter Kelvin when working with gas laws (like the Ideal Gas Law PV = nRT, where T must be in Kelvin), blackbody radiation, colour temperature for lighting, and cryogenic applications. Everyday weather and cooking use Celsius or Fahrenheit, but scientific calculation almost always requires Kelvin.
Add 273.15 to the Celsius temperature. K = °C + 273.15. For example, 100°C = 100 + 273.15 = 373.15 K (the boiling point of water). To convert back, subtract 273.15.
Absolute zero is 0 K, which equals −273.15°C. It is the theoretical minimum temperature — the point at which all molecular kinetic energy is zero. It is physically impossible to reach temperatures below 0 K.
The Kelvin scale starts at absolute zero (0 K), the lowest physically possible temperature. Since nothing can be colder than a state of zero molecular motion, there are no negative values on the Kelvin scale.
0°C (the freezing point of water at standard pressure) equals 273.15 K. Similarly, 100°C (the boiling point) equals 373.15 K, and normal body temperature (37°C) equals 310.15 K.
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