Temperature Converter

Convert between Celsius, Fahrenheit, and Kelvin, with the formulas and reference points behind each scale explained.

The Three Temperature Scales Explained From First Principles

Temperature scales differ not just in their numbers but in what they’re actually anchored to. Celsius is anchored to water, with zero degrees set at water’s freezing point and one hundred degrees at its boiling point at standard atmospheric pressure, making it intuitive for everyday and scientific use since those reference points are easy to reproduce anywhere. Fahrenheit, still used for everyday temperature in the United States, was anchored differently by its creator, originally to a brine solution’s freezing point at zero and human body temperature near ninety-six, though the scale was later refined so that water freezes at thirty-two degrees and boils at two hundred twelve, an oddly specific pair of numbers that makes the conversion formula between Celsius and Fahrenheit look more complicated than it really is: multiply Celsius by nine-fifths and add thirty-two to get Fahrenheit, or subtract thirty-two and multiply by five-ninths to go the other way. Kelvin is the odd one out entirely, because it isn’t anchored to water at all but to absolute zero, the theoretical point at which molecular motion stops completely, making zero Kelvin the coldest temperature physically possible. Kelvin uses the same size degree as Celsius, just shifted, so converting between the two is simply a matter of adding or subtracting 273.15, which is why Kelvin is the scale of choice in physics and engineering, where working with negative numbers for everyday cold temperatures is genuinely inconvenient.