I would assume that the Pridelands are a rough circle about five miles in radius.
On flat ground (or the ocean), you can only see three miles until the horizon due to the curvature of the Earth. However, the Pridelands are not flat, hurting the distance. At the same time, the horizon is taken from the top of Priderock, which is about fifty feet up. So this is why I give the rough estimate of a five mile radius.
This makes the entire kingdom have an area of about 78.5 square miles. This is about 50,240 acres. A respectable size, to say the least.