Converte
Temperature
0 °C is 32 °F. 100 °C is 212 °F. −40 is the same number on both scales.
How it works
Fahrenheit to Celsius: subtract 32, then multiply by 5/9. The reverse multiplies by 9/5 and adds 32. Kelvin is Celsius plus 273.15.
Doubling the number on a scale does not double a temperature difference unless you are already counting from absolute zero. This page converts the thermometer mark.
Questions
Why is 1 °C not 1 °F?
The span from freezing to boiling is 100 degrees Celsius and 180 degrees Fahrenheit. One Celsius degree is 1.8 Fahrenheit degrees.
Can kelvin be negative?
Not as a physical temperature. The arithmetic still runs. Below 0 K the number is not a temperature.
Is “subtract 30 and halve” good enough?
Only as a rough middle-of-the-scale guess. Not for a fever or a recipe.