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How to Convert Celsius and Fahrenheit in Your Head

If you travel or follow a recipe from another country, these shortcuts help you sense a temperature in seconds.

Try the Celsius to Fahrenheit ConverterFree, no sign-up. Uses the same formulas explained below.

The exact formulas

  • Fahrenheit = Celsius × 9/5 + 32
  • Celsius = (Fahrenheit − 32) × 5/9

The quick estimate from °C to °F

Double the Celsius number and add 30. For 20 °C: 40 + 30 = 70 °F. The exact answer is 68 °F, so it is close for weather.

The quick estimate from °F to °C

Subtract 30 and halve it. For 72 °F: 42 ÷ 2 = 21 °C, against the exact 22.2 °C.

Temperatures worth knowing

  • 0 °C = 32 °F: water freezes
  • 20 °C = 68 °F: a comfortable room
  • 30 °C = 86 °F: a hot day
  • 37 °C = 98.6 °F: normal body temperature
  • 100 °C = 212 °F: water boils at sea level

For cooking, use the exact formula

Shortcuts are fine for weather, but for baking use the converter so your oven is set correctly.

Frequently asked questions

At what temperature are Celsius and Fahrenheit equal?

At −40. Both scales give the same number there.

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