Explanation
Oven settings in °C and °F
Recipes give oven temperatures in Celsius or Fahrenheit, and many assume a conventional oven. Convert between the scales exactly, or lower a conventional setting for a fan (convection) oven by the amount your recipe or oven manual suggests.
F = C × 9/5 + 32
| C | Temperature in Celsius (°C) |
|---|---|
| F | Temperature in Fahrenheit (°F) |
A 180 °C cake recipe on a Fahrenheit oven
| Temperature | 180 |
|---|---|
| Result | 356 °F |
F = C × 9/5 + 32 = 180 × 9/5 + 32 = 356 °F
C = (F − 32) × 5/9
| F | Temperature in Fahrenheit (°F) |
|---|---|
| C | Temperature in Celsius (°C) |
356 °F back to Celsius
| Temperature | 356 |
|---|---|
| Result | 180 °C |
C = (F − 32) × 5/9 = (356 − 32) × 5/9 = 180 °C
T′ = T − r
| T | Conventional setting (°C) |
|---|---|
| T′ | Fan oven setting (°C) |
| r | Reduce by (°C) |
A 180 °C recipe in a fan oven, reduced by 20 °C
| Conventional setting | 180 |
|---|---|
| Reduce by | 20 |
| Result | 160 °C |
T′ = T − r = 180 °C − 20 °C = 160 °C
Diagram of this result
For a conversion, two rulers share one marker: Celsius above, Fahrenheit below. For a fan oven, one Celsius scale shows the conventional setting, the fan setting and the gap between them.
The temperatures in the diagram are the same numbers stated in the answer and the steps.
Common mistakes
Pick the direction first: 180 °C is 356 °F, but 180 °F is only 82 °C. Subtract a fan reduction from the Celsius setting, not from Fahrenheit; a 20 °C reduction is 36 °F. Oven dials are rarely exact, so an oven thermometer helps more than extra decimals.
Assumptions and limits
Conversions are exact. Temperatures may be negative down to absolute zero (−273.15 °C or −459.67 °F). The fan reduction is a recipe or appliance convention you enter, commonly 20 °C; it is not a physical constant, and the adjusted setting cannot fall below absolute zero. Answers are shown to the nearest degree.
How much lower should a fan oven be?
Most recipes and manufacturers suggest about 20 °C lower, for example 160 °C fan instead of 180 °C conventional. Check your oven manual, as some fan ovens already compensate automatically.
Sources
Temperature scale definitions: NIST SP 811, https://www.nist.gov/pml/special-publication-811.