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Celsius to Kelvin Calculator

Convert Celsius to Kelvin for science and engineering.

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Enter your values and click Calculate

How It Works

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.

Examples

Room Temperature
A typical room temperature of 25°C.
Result: 25°C equals 298.15 K.
Absolute Zero
The coldest possible temperature: −273.15°C.
Result: −273.15°C equals 0 K (absolute zero).
Boiling Point of Water
Water boils at 100°C.
Result: 100°C equals 373.15 K.

Frequently Asked Questions

What is the formula for Celsius to Kelvin?
The formula is K = °C + 273.15. The offset of 273.15 represents the distance between the Celsius zero point (the freezing point of water) and absolute zero. Because the Kelvin and Celsius degree sizes are identical, only an addition is needed — no scaling factor.
Why does Kelvin start at absolute zero?
Kelvin was designed as a thermodynamic scale where 0 K represents the complete absence of thermal energy — the lowest possible temperature in the universe, at which all molecular motion ceases. This makes Kelvin invaluable in physics and chemistry because it eliminates negative temperatures, allowing equations like the ideal gas law (PV = nRT) to work correctly without special handling for sub-zero values.
Does Kelvin use a degree symbol?
No. Kelvin values are written without a degree symbol — for example, 300 K, not 300°K. This convention reflects the fact that Kelvin is an absolute thermodynamic scale rather than a relative one like Celsius or Fahrenheit. The unit is simply called 'kelvin' (lowercase), and the SI symbol is K.

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