Why temperature needs formulas, not just a factor
Length and weight scale from zero, so a single multiplier is enough. Temperature scales have different zero points. Celsius puts zero at the freezing point of water, Fahrenheit sets it at the coldest brine mixture of the 1700s, and Kelvin starts at absolute zero, the lowest possible temperature. Converting therefore needs an offset as well as a multiplier. This tool converts every scale into Kelvin first and then into the scale you chose, which keeps all the formulas consistent.
The formulas
- Celsius to Fahrenheit: °F = °C × 9/5 + 32. So 100 °C is 212 °F, and 37 °C is 98.6 °F.
- Fahrenheit to Celsius: °C = (°F − 32) × 5/9. So 72 °F is about 22.2 °C.
- Celsius to Kelvin: K = °C + 273.15. Absolute zero is 0 K, or −273.15 °C.
- Fahrenheit to Rankine: °R = °F + 459.67. Rankine is a scale used in some engineering fields in the United States.
Useful reference points
Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at standard sea-level pressure. Normal human body temperature is around 37 °C (98.6 °F), though healthy readings vary between people and over the day. A comfortable room is often quoted as 20 °C to 22 °C (68 °F to 72 °F). Oven recipes often use 180 °C, which is 356 °F, usually written as 350 °F in American recipes. The two scales give the same number at −40, which is a quick check for your arithmetic.
Mental shortcuts
For a rough Celsius to Fahrenheit estimate, double the Celsius number and add 30. It is off by a few degrees but good enough for weather. For Fahrenheit to Celsius, subtract 30 and halve. When accuracy matters, as in cooking sugar, lab work or setting a thermostat, use the exact result from the tool.
Notes on precision
A temperature difference converts differently from a temperature reading: a rise of 10 °C is a rise of 18 °F, without adding 32. This tool converts readings, not differences. Values below absolute zero are not physically possible, but the tool does not block them, so check your input. Everything is computed in your browser and nothing is sent anywhere.