Formula · temperature

Fahrenheit to Celsius Formula

Convert any Fahrenheit temperature back to Celsius by undoing the +32 offset and 9/5 scale.

Quick answer

Formula

°C = (°F − 32) × 5/9

How it works

The two scales disagree about both where zero sits and how big one degree is, so the conversion has to fix both. Subtracting 32 moves Fahrenheit's freezing point onto Celsius's zero. Multiplying by 5/9 then shrinks the step size, because there are 180 Fahrenheit degrees between the freezing and boiling points of water where Celsius has 100, and 100/180 reduces to 5/9. The order matters: subtract first, then scale. Doing it the other way round leaves every answer wrong by the same 14.2 degrees, whatever temperature you started with.

Variables

°CTemperature in Celsius (result)
°FTemperature in Fahrenheit (input)

Worked examples

Input	Result
32 °F	0 °C
212 °F	100 °C
70 °F	21.1 °C (room temperature)

Practical applications

Reading a US weather forecast or oven setting from outside the US
Converting a body temperature reading - 98.6 degrees F is 37 degrees C
Interpreting older engineering and meteorological records, which are frequently Fahrenheit

Common mistakes

Scaling before subtracting. (F x 5/9) - 32 is not the same as (F - 32) x 5/9.
Using 1.8 as though it were an offset rather than a ratio.
Applying the same formula to a temperature difference. A change of 18 degrees F is a change of 10 degrees C - for differences you scale by 5/9 and do not subtract anything, because the offset cancels.