[philipps]

20 C > 68 F

30 C > 86 F

[susam]

-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.

[wiredfool]

16=61. Much more useful summer conversion temperature in Ireland.