Marika,
Sadly the conversion isn't that simple.
The formula is:
(('degrees fahrenheit' - 32) x 5) / 9
that is
(81 -32) x 5 divided by 9 = 27.22 degrees C
Thankfully, us oldies are slowly being converted too and I think Fahrenheit will be soon like 'shillings and pence' - forgotten!! lol.