Convert degrees Celsius to Fahrenheit

Fahrenheit is used in the United States for weather, ovens and body temperature, so the conversion comes up constantly when travelling or following recipes.

Unlike other conversions, multiplying is not enough here: the two scales have different zero points. First multiply by 1.8, then add 32 degrees.

The two scales cross at one point

At forty below zero, Celsius and Fahrenheit read the same: −40 °C is −40 °F. It is the only value where they coincide, and it works as a quick check that a formula has been applied correctly.

Why Fahrenheit has such odd numbers

Fahrenheit set zero at the temperature of a mixture of ice, water and ammonium chloride, the coldest he could reproduce in his laboratory in 1724, and put human body temperature near 96. With that reference, the freezing point of water landed on 32 and boiling on 212. Celsius, half a century later, started from water directly: 0 and 100.

Where each is used

Fahrenheit survives in the United States, its territories and a few Caribbean countries. The rest of the world uses Celsius. Scientific work uses the kelvin, which has the same degree size as Celsius but starts at absolute zero, −273.15 °C.

Temperature difference versus temperature

To convert a difference, do not add the 32: a rise of 10 °C equals a rise of 18 °F, not 50. It is a frequent mistake when reading technical tolerance specifications.