I had another question about this but can't remember where I answered it so will merge it here when I find it.
The short answer Ellie is that there is no hard and fast size for a peregrine territory - depends on what features are available - nest ledges, roosts, feeding places, courting places etc as well as the environment/habitat, the amount of prey, the number of other birds nearby ... you get the idea. Urban nestsites can be larger and smaller than wild nestsites.