Kelvin to Celsius

Kelvin values appear in papers, data sheets and news about space, and turning them into Celsius makes them feel real. The cosmic microwave background, the afterglow of the Big Bang, is 2.725 K, which is −270.4 °C. Liquid nitrogen boils at about 77 K, roughly −196 °C, and liquid helium at about 4.2 K, close to −269 °C. The surface of Venus averages around 737 K, about 464 °C, hot enough to melt lead.

The Sun's visible surface has an effective temperature of 5,772 K, which the converter turns into roughly 5,499 °C. At such large values the 273.15 offset hardly matters, and many writers round it, but the exact subtraction keeps your figures consistent.

Light bulbs, monitors and camera white balance use kelvin for color temperature: 2,700 K is warm white, 4,000 K neutral and 5,000 to 6,500 K daylight. This describes the color an ideal glowing body would have at that temperature, not how hot the bulb is. Converting a 2,700 K LED to 2,427 °C is arithmetically correct but physically meaningless, since the bulb runs at well under 100 °C.

Lower color temperature looks warmer and redder, which is the opposite of how heat feels, so it is better to treat those numbers as color labels.

Anything below 273.15 K is below freezing in Celsius, and anything below 373.15 K is below the boiling point of water at sea-level pressure. A difference in kelvin equals the same difference in Celsius: a material that warms by 15 K has warmed by 15 °C.

For the opposite direction, Celsius to kelvin adds the offset back. For Fahrenheit, convert here first and then use Celsius to Fahrenheit.