Temperature Converter
Temperature is the one conversion where multiplying by a factor is not enough — the scales start in different places, so an offset has to be applied before and after scaling.
Temperature to Convert
Values below absolute zero are flagged rather than silently converted.
All units
The same quantity expressed every other way.
Why temperature conversion is not just multiplication
Converting metres to feet is a single multiplication because both scales start at the same zero. Temperature scales do not. Celsius puts zero at the freezing point of water; Fahrenheit puts zero roughly at the freezing point of a brine mixture; Kelvin puts zero at absolute zero. Converting therefore requires shifting the origin as well as changing the step size, which is why the familiar formula has both a multiplier and a constant.
The one temperature where both scales agree
Celsius and Fahrenheit cross at −40. It is the only point where the two scales give the same number, and it is a useful sanity check — if a conversion tool does not return −40 °F for −40 °C, something is wrong with its offset handling.
Degrees versus kelvins
Kelvin is written without the degree symbol: 300 K, not 300 °K. That is because Kelvin is an absolute scale where zero means zero thermal energy, so a kelvin is a unit of temperature rather than a point on a relative scale. The same applies to a temperature difference: a rise of one kelvin equals a rise of one degree Celsius exactly, which is why scientific papers often report differences in kelvins even when the absolute values are in Celsius.
Absolute zero as a floor
Nothing can be colder than −273.15 °C, or −459.67 °F, or 0 K. This converter flags values below that floor instead of quietly converting them, because a negative kelvin result is always a data-entry mistake rather than a physical measurement.