The conversion
40°C = 104°F
°F = (°C × 9/5) + 32, so (40 × 9/5) + 32 = 104.
As an outdoor air temperature, 40 °C sits in the hot 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.
| Celsius | Fahrenheit |
|---|---|
| 35 °C | 95 °F |
| 36 °C | 96.8 °F |
| 37 °C | 98.6 °F |
| 38 °C | 100.4 °F |
| 39 °C | 102.2 °F |
| 40 °C | 104 °F |
| 41 °C | 105.8 °F |
| 42 °C | 107.6 °F |
| 43 °C | 109.4 °F |
| 44 °C | 111.2 °F |
| 45 °C | 113 °F |
The other direction
104 °F converts back to 40 °C, which is the same relationship read the other way. Going from Fahrenheit to Celsius, subtract 32 first and then multiply by 5/9 — doing it in the other order is the usual mistake and produces a plausible-looking wrong answer.
The full converter handles any value, in either direction, including kelvin, and shows the formula as it works.