Temperature Converter
Convert Celsius, Fahrenheit and Kelvin.
Good to know. −40 is the same in Celsius and Fahrenheit. It’s also too cold in both.
How it works
In plain words
To go from Celsius to Fahrenheit, multiply by 9/5 and add 32. To go back, subtract 32 and multiply by 5/9. Kelvin is Celsius plus 273.15.
The formula
°F = °C × 9 ÷ 5 + 32 °C = (°F − 32) × 5 ÷ 9 K = °C + 273.15
Worked example
20 °C × 9 ÷ 5 = 36, and 36 + 32 = 68 °F. A mild spring day.
Sources
- BIPM, The International System of Units (SI Brochure), 9th edition
- NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B Exact conversion factors for US customary units.
Sources checked September 29, 2026. 8 automated tests check its answers on every change.
About the temperature converter
Temperature is the one common conversion that is not a simple multiplication, because the scales start from different zero points. Water freezes at 0 °C, which is 32 °F, and boils at 100 °C, which is 212 °F (at sea level). So there are 180 Fahrenheit degrees between freezing and boiling, but only 100 Celsius degrees. That gives the 9/5 factor, and the 32 comes from the different starting points.
A quick mental estimate from Celsius to Fahrenheit: double it and add 30. It is close for everyday weather (20 °C gives 70, versus the exact 68). Going the other way, subtract 30 and halve.
Some useful reference points: normal body temperature is about 37 °C (98.6 °F), and a fever is usually taken to start at 38 °C (100.4 °F). A typical oven setting of 180 °C is 356 °F, usually rounded to 350 °F in recipes. At −40, the two scales meet: −40 °C is −40 °F.
Kelvin is the scientific scale. It starts at absolute zero, the coldest possible temperature, and its degrees are the same size as Celsius degrees. It is written without the degree sign: 0 °C is 273.15 K.
Questions people ask
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (or 1.8) and add 32. 20 °C is 68 °F.
How do I convert Fahrenheit to Celsius?
Subtract 32 and multiply by 5/9. 100 °F is about 37.78 °C.
What is 180 °C in Fahrenheit?
356 °F. Recipes usually round it to 350 °F (gas mark 4).
At what temperature are Celsius and Fahrenheit equal?
At −40. −40 °C is exactly −40 °F.