Celsius Converter

Celsius is an affine temperature scale with two fixed points: water freezes at 0 °C and boils at 100 °C at one atmosphere. It is not a multiplier applied to a quantity.

Celsius is the everyday scale for weather reporting, cooking and oven settings, refrigeration, medicine and most laboratory and engineering work, and it is the working scale wherever metric measures are used.

Celsius is an offset scale, so a Fahrenheit value cannot be converted by multiplying by 1.8 alone; 32 must be added or subtracted. Absolute zero is −273.15 °C, which is 0 K.

A common error is quoting a body temperature in Fahrenheit without noting that this site is Celsius-first, so 98.6 °F appears as 37 °C here. The two scales meet only at −40.

Celsius and Fahrenheit share the weather, oven and body-temperature roles, so a bare number is ambiguous; 30 means a hot day in Celsius and a cold one in Fahrenheit. Kelvin takes over in scientific work where absolute values matter.

Celsius to Kelvin is the only temperature pair that behaves like a simple conversion: same degree size, different zero, so the value shifts by 273.15 and no multiplication is involved. Every pair involving Fahrenheit is affine, meaning a scale factor and an offset applied together.

That is why this dimension is the exception to the rest of the converter. Multiplying a Celsius figure by 9/5 gives a number that is not a Fahrenheit temperature, because the 32-degree offset is still missing. The result only becomes correct when the addition is made in the right order.

Checking a temperature conversion is easiest at a value whose answer you know: water freezing and boiling, body temperature, or the single reading of −40 where the Celsius and Fahrenheit scales agree. The error to watch for is dropping the offset when converting a temperature difference, where it genuinely does not apply.