Fahrenheit Converter

Fahrenheit is an affine temperature scale that fixes the freezing point of water at 32 °F and the boiling point at 212 °F at one atmosphere, matching 0 °C and 100 °C.

Fahrenheit remains the everyday scale for weather reporting, cooking oven settings and body temperature in the United States, while science, medicine and most other countries report temperatures in Celsius.

Because Fahrenheit is an offset scale, subtracting 32 first is required; multiplying by 5/9 alone gives a wrong answer. One Fahrenheit degree is five ninths of a Celsius degree.

A frequent mistake is reading a Fahrenheit figure as Celsius, which makes an 80 °F day look like 80 °C on a Celsius-first site. The two scales agree at exactly −40, the single point where both read the same.

Fahrenheit and Celsius are applied to the same jobs, so an oven setting and a weather reading can be misread when the scale is dropped. Kelvin is the third scale, and it stays in scientific use.

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.