Celsius to Kelvin Calculator

Kelvin is the SI base unit of temperature, fundamental to physics, chemistry, thermodynamics, and engineering. Unlike Celsius and Fahrenheit, the Kelvin scale starts at absolute zero — the lowest theoretically possible temperature, at which all molecular motion ceases. Converting from Celsius to Kelvin is a routine step in scientific calculations: the ideal gas law (PV = nRT), black-body radiation equations, thermodynamic efficiency formulas, and many other physics equations require temperature in Kelvin because they break down mathematically when temperatures near or cross zero. Chemists use Kelvin for reaction rate calculations. Astronomers measure stellar temperatures in thousands of Kelvin. Electrical engineers use it in noise calculations. Any time you see a temperature expressed in scientific notation in a physics or chemistry textbook, it is almost certainly in Kelvin. Room temperature is approximately 293–298 K, the boiling point of water is 373.15 K, and absolute zero is 0 K (equivalent to −273.15°C).

The conversion formula is: K = °C + 273.15. The offset 273.15 is not arbitrary — it is the exact value of absolute zero expressed in degrees Celsius. Since the Kelvin and Celsius scales have identical degree sizes (a temperature difference of 1 K equals a difference of 1°C), converting between them requires only a shift of the zero point, not a scaling factor. The value 273.15 comes from the international definition of the Kelvin: the triple point of water (where liquid, solid, and gas coexist in equilibrium) is defined as exactly 273.16 K, and the freezing point of water is approximately 273.15 K (0.01 K below the triple point). This simple addition makes it exact: 0°C + 273.15 = 273.15 K, 100°C + 273.15 = 373.15 K, −273.15°C + 273.15 = 0 K (absolute zero). No other arithmetic is needed.