Site dimensions, topography, and vehicle type affect the design of parking lots. For planning purposes, as a general rule, assume approximately 300-350 square feet is required per parking space. This allotment will account for traffic aisles, end island/caps, space between adjacent cars, as well as the entrance and exit lanes.
As an example, assume the given lot is 100 ft by 100 ft, which equates to a total square footage of 10,000 SF. The resultant of 10,000 divided by 325 is approximately 30 - - implying the final design of the parking lot should accommodate about 30 vehicles.