4 ms·20 C > 68 F 30 C > 86 Fby philipps 7y ago20 C > 68 F 30 C > 86 Fsusam 7y ago-40 °C = -40 °F. A related joke: Saul: It's -40 outside. Paul: Fahrenheit or Celsius? Saul: When it's that cold, it's impossible to tell the difference.deleted 7y ago[deleted]wiredfool 7y ago16=61. Much more useful summer conversion temperature in Ireland.