The formula
°C = (°F − 32) × 5/9. Take off 32 first, because that is where water freezes on the Fahrenheit scale, then multiply by 5/9 (about 0.5556) because each Fahrenheit degree is smaller. For 68 °F: 68 − 32 = 36, and 36 × 5/9 is 20 °C. Multiplying before subtracting gives the wrong answer.
Oven and weather temperatures
Rounded to one decimal place:
| Fahrenheit | Celsius |
|---|---|
| 0 °F | −17.8 °C |
| 32 °F | 0 °C |
| 50 °F | 10 °C |
| 68 °F | 20 °C |
| 86 °F | 30 °C |
| 98.6 °F | 37 °C |
| 212 °F | 100 °C |
| 350 °F | 176.7 °C |
| 400 °F | 204.4 °C |
| 450 °F | 232.2 °C |
Oven dials in Celsius usually step by 10 or 20, so 350 °F (176.7 °C) is set as 180 °C and 400 °F (204.4 °C) as 200 °C.
Questions
How cold is 0 °F?
−17.8 °C. Daniel Fahrenheit set his zero by a freezing mix of ice, water and salt, which is why it does not line up with anything on the Celsius scale.
Is there a quick way to do it in my head?
Take off 30 and halve it: 80 °F gives 25 against the real 26.7 °C. It stays within 2 degrees from about 15 °F to 85 °F.