Celsius to Kelvin

Celsius to Kelvin in Depth

Add 273.15 — the entire conversion. But the meaning matters more: Kelvin starts at absolute zero, the coldest physically possible temperature, so there are no negative Kelvins and ratios become meaningful (400 K is truly twice as hot as 200 K; 40°C is not twice 20°C).

Why Science Insists on Kelvin

Gas laws, thermodynamics, and blackbody radiation all require an absolute scale — the formulas literally break with Celsius's arbitrary zero. Any equation with temperature multiplied or divided wants Kelvin.

Reference Points

Water freezes at 273.15 K, boils at 373.15 K; room temperature is ~293 K; the Sun's surface is ~5,778 K. The triple point of water (273.16 K) once defined the Kelvin.