Frequently asked question.
There's another thread on her somewhere from a few months back where there were lots of replies - but I can't find it.
How long is a piece of string? It depends on a number of things :-
a) what air-con unit you have i.e. power consumption
b) what temp you set it on
c) when you last had it serviced (i.e. are the filters clogged up)
d) whether you are leaving the doors and windows open
In VERY simple terms - if the filters are clean and you have the doors and windows shut, for the one we have in our apartment:-
If you set it on 25c then it will use 2-3 units per hour (and this temp is very comfortable)
If you set it on 16c then it actually won't cool down things down much further, the unit will work much harder and you will use a lot more electricity - probably 4 units per hour.