How many do I need???

We will probably be moving in a few months and I have bought Zero to spray on the apartment carpets (just in case any other residents animal has ever "done anything" there)....and I got some spray from the vet for the carpets in case there are any fleas....but I want to get some FELIWAY defusers. The apartment is just under 1,000 feet square.... I was thinking 3, one at each end of the apt, and one fairly centrally located (which would be in the bathroom where the litter box will be) What do you think?
I want this move to be as easy and uneventful for our 3 "boys" as possible.
Thanks! Linda

I think the box says one for every 700 sq ft. I have one in our 648 sq ft apartment.

Thanks for the info....I found a deal on the net for 3/$75 (ship & hand incl) so guess i`ll start out with 2 and save the 3rd one for if I ever need it for another time.
Linda