25°C is 77°F: reading a forecast in the other scale
· 3 min read
A forecast of 25°C is 77°F. That is a warm day, not a mild one. If you grew up with one scale and the forecast is in the other, the quickest fix is a handful of anchor points and one rough rule.
The anchor points
Every 10 degrees Celsius is 18 degrees Fahrenheit, starting from freezing at 0°C and 32°F:
The words beside each figure are a rough guide. How a temperature feels depends on wind, humidity and sun, which no conversion knows. The temperature converter gives the exact figure for any reading.
Double it and add 30
The exact sum is to multiply by 1.8 and add 32. In your head, doubling and adding 30 is close enough for a forecast:
- 10°C: the shortcut gives 50°F, which is exact.
- 20°C: the shortcut gives 70°F. The real figure is 68°F.
- 30°C: the shortcut gives 90°F. The real figure is 86°F.
- 40°C: the shortcut gives 110°F. The real figure is 104°F.
The shortcut is exact at 10°C and drifts by 2 degrees for every 10 above it. It is fine for deciding what to wear and wrong for an oven.
Going the other way
From Fahrenheit, take away 30 and halve. 70°F becomes 20°C by the shortcut, and the real figure is 21.1°C. 90°F becomes 30°C, and the real figure is 32.2°C. The same drift, in the other direction.
What this leaves out
- How it feels. A forecast often gives a second “feels like” figure for wind or humidity. That is the forecaster’s estimate, not a conversion.
- The night. A daytime high says little about the evening. Look at the low as well.
- Cooking. Oven temperatures need the exact figure. The oven temperature converter is for that.
The conversions are exact. The shortcut is not, by the amounts shown.
