Celsius to Fahrenheit

How this is calculated

Multiply the Celsius temperature by 9/5, which is 1.8, then add 32: °F = °C × 9/5 + 32. For 20 °C: 20 × 1.8 = 36, and 36 + 32 = 68 °F. The formula is exact. A step of one degree Celsius is 1.8 degrees Fahrenheit, and 0 °C is 32 °F (NIST Special Publication 811).

For a quick estimate in your head, double the Celsius and add 30. At 10 °C that gives 50 °F, exactly right; at 30 °C it gives 90 °F, while the exact answer is 86 °F. The estimate stays within 2 degrees between 0 and 20 °C and drifts further outside that range.

Kelvin, the scale of science, starts at absolute zero: K = °C + 273.15. Absolute zero is −273.15 °C or −459.67 °F, and nothing gets colder.

Body temperature

MedlinePlus gives 98.6 °F (37 °C) as the generally accepted average body temperature and notes that studies find a range from about 97 °F to 99 °F (36.1 °C to 37.2 °C). The CDC defines a fever as a measured temperature of 100.4 °F (38 °C) or higher.

Oven temperatures

A recipe written in Celsius needs converting before you set a U.S. oven. The last column rounds to the nearest 25 °F: 180 °C is exactly 356 °F, and the nearest 25 °F is 350 °F.

Temperatures worth knowing

Food-safety charts print rounded Celsius values: FoodSafety.gov lists 165 °F as 74 °C and 145 °F as 63 °C, and the FDA gives 40 °F as 4 °C and 0 °F as −18 °C. Water freezes at 0 °C and boils at 100 °C at normal sea-level air pressure; at higher altitude it boils at a lower temperature.