🌡️ Temperature & ovens
100 °F to °C
100 °F is 37.8 °C. Subtract 32, multiply by 5 and divide by 9. On a fan oven, set about 18 °C.
The short answer
100 °F = 37.8 °C
Fan oven: 18 °C. This is a very low oven.
About 100 °F in °C
100 °F is 37.8 °C. The formula is (F − 32) × 5/9: 100 − 32 = 68, then 68 × 5 ÷ 9 = 37.8. Celsius and Fahrenheit cross at − 40, not at zero, which is why the subtraction comes first.
Fan ovens run about 20 °C cooler than the temperature written on a conventional recipe, so a 100 °F instruction becomes 18 °C on a fan setting. If your oven only has round numbers, choose the nearest (40 °C) and adjust the time by about 10%.
A 100 °F oven is in the very low band — roughly gas mark ¼. That matters more than the exact degree: a 10 °C error changes a sponge by a couple of minutes, while the wrong band changes whether the outside browns before the middle sets.
Gas marks are a third scale in the same kitchen: 100 °F, 38 °C and a gas mark all describe one oven heat, and British recipes still print two of the three side by side. Converting 100 °F to 38 °C and then to a fan setting of 18 °C keeps the recipe's intent even when your oven runs a little hot.
Recipe apps often write the question as 100 f to c rather than with degree symbols, and the answer is the same: 37.8 c. Rounded to 38 c, that is what most oven dials can actually be set to.
How the calculation works
- (100 °F − 32) × 5/9 = 37.8 °C
- Fan oven: 37.8 − 20 = 17.8 °C
- Reverse: (37.8 °C × 9/5) + 32 = 100 °F
Reference values
| Fahrenheit | Celsius | Fan oven |
|---|---|---|
| 50 °F | 10 °C | -10 °C fan |
| 75 °F | 24 °C | 4 °C fan |
| 100 °F | 38 °C | 18 °C fan |
| 125 °F | 52 °C | 32 °C fan |
| 150 °F | 66 °C | 46 °C fan |