Celsius to Fahrenheit Converter

The popular mental trick is to double the Celsius figure and add 30. It's exact at 10 °C and drifts further off the further you go from there, because it uses 2 instead of 1.8:

So it's good enough to decide whether you need a jacket, but never use it for a thermometer reading or an oven.

To get the precise answer without a calculator, double the number, take away a tenth of the result, then add 32. That's the same as multiplying by 1.8.

• 180 °C: double to 360, minus 36 gives 324, plus 32 is 356 °F.
• 37 °C: double to 74, minus 7.4 gives 66.6, plus 32 is 98.6 °F.
• 25 °C: 50, minus 5 is 45, plus 32 is 77 °F.

Whole Celsius numbers that are multiples of 5 always give whole Fahrenheit numbers. Anything else gives a decimal, which is why 22 °C comes out as 71.6. If a recipe says 180 °C, set the oven to the nearest mark your dial has to 356 °F.

Below zero, type the minus sign: −20 °C is −4 °F, and −40 is the one point where both scales read the same.

When a forecast says it will be 3 °C warmer tomorrow, the change in Fahrenheit is 3 × 1.8 = 5.4 °F. Don't add 32 to a difference. If you type 3 into the converter you get 37.4 °F, which is the reading 3 °C, not a rise of 3 degrees.

The same goes for any gap between two temperatures: a 5 °C range in a weather report is 9 °F, and a 10 °C range is 18 °F. Convert both readings and subtract, or multiply the difference by 1.8.