Celsius to Fahrenheit

The Swedish astronomer Anders Celsius proposed his scale in 1742 with 0 at the boiling point of water and 100 at freezing; it was flipped to the familiar direction shortly after his death. It was called centigrade for two centuries until an international conference renamed it the degree Celsius in 1948. Today it is tied to the kelvin, which has been defined through the Boltzmann constant since 2019: a temperature in °C is simply the kelvin value minus 273.15.

Daniel Gabriel Fahrenheit built his scale around 1724, using a freezing brine mixture for zero. The two scales differ in both step size and starting point, which is why the formula has two parts. Water freezes at 0 °C or 32 °F and boils at 100 °C or 212 °F at sea level, so 100 Celsius degrees span 180 Fahrenheit degrees, giving the 9/5 ratio. Only at −40 do the two read the same number.

Normal body temperature is usually given as 37 °C, which is 98.6 °F. A fever generally starts at 38 °C, or 100.4 °F, and 39.5 °C is 103.1 °F, the point where many parents call a doctor for a child. A comfortable room at 21 °C is 69.8 °F, a hot summer day at 35 °C is 95 °F, and a cold winter morning at −10 °C is 14 °F.

Ovens are where travelers and recipe readers convert most. European recipes say 180 °C for cakes, which is 356 °F; American recipes round the same setting to 350 °F. 200 °C is 392 °F and 220 °C, a typical roasting heat, is 428 °F. For the opposite direction, see Fahrenheit to Celsius.

Double the Celsius figure and add 30 for a fast estimate. It is spot-on at 10 °C (50 °F) and drifts as you move away: 30 °C gives 90 against the exact 86 °F. Good enough for deciding on a jacket, not for a fever or a sugar thermometer.

The common error is adding 32 before multiplying; always multiply first. The other is converting a change in temperature with the full formula. A rise of 10 °C is a rise of 18 °F, not 50 °F, because differences only scale by 1.8 and the 32 offset cancels out. Kelvin and other temperature pairs are in the unit converter.