You are opening yourself to a massive headache. If you put a calculator on your website and people use it to work out how much it is going to cost them, then that is what they will want to pay you regardless of any "this is an estimate only" blurb you put at the bottom.
If I booked you and you said it was going to be more than the calculator stated, I would want to know why?
If you said it's because "my carpets were heavily soiled" or "there was furniture to move" or "it was three floors up". My reply would be that I never got asked those questions on the calculator so to me they must be irrelevant, I will pay what the calculator says I should pay.
Personnally I would make it simpler, have a fixed price for a single carpet up to a certain size, then a price for larger areas.
Just put in to clean three rooms all 4m x5m, come to £59.07 (£19.69/room)