The conversion
66°F = 18.89°C
°C = (°F − 32) × 5/9, so (66 − 32) × 5/9 = 18.89.
As an outdoor air temperature, 66 °F sits in the mild band. The other scale is on the dial beside it in the app, so a reading like this needs no conversion at all.
Convert something else
68°F
The range either side
Neighbouring values, for when the number you actually wanted was a degree or two away.
| Fahrenheit | Celsius |
|---|---|
| 61 °F | 16.11 °C |
| 62 °F | 16.67 °C |
| 63 °F | 17.22 °C |
| 64 °F | 17.78 °C |
| 65 °F | 18.33 °C |
| 66 °F | 18.89 °C |
| 67 °F | 19.44 °C |
| 68 °F | 20 °C |
| 69 °F | 20.56 °C |
| 70 °F | 21.11 °C |
| 71 °F | 21.67 °C |
The other direction
18.89 °C converts back to 66 °F, which is the same relationship read the other way. Going from Celsius to Fahrenheit, multiply by 9/5 first and then add 32. Adding first is the usual mistake.
The full converter handles any value, in either direction, including kelvin, and shows the formula as it works.