What is the size of the vehicles?

Just assume the vehicles are 15"x5", which is 75 square feet. So at the most, you can shove 160 vehicles in there. It'll be like 8 bitches on a bitch boat trying to get them out of there, though.

A back of the hand calculation would be as follows: 12000sqf = 110' x 110' parking lot (square) approximate Let's assume 9' wide parking spaces that are 18.5' deep and separated by 26' of drive path. The width of one row of car/path/car would be 63' (18.5' + 26' + 18.5'). Let's double this and say that there is a one way drive path, a row of parked cars, a two way drive path with cars on each side, and another one way drive path with one side of parked cars. So you'll have: half path/car/car/full path/car/car/half path. This would give you 63' x 2 for the width now which is 126'. You could park 4 cars in one row that is 126' wide x 9' deep. Take your original sqf of 12000 and divide by 126' and you get approximately 95' as your lot width. At 9' wide per row, you could fit 10 rows and still have room (5') for a sidewalk or pedestrian in the middle of the lot. 10 rows x 4 cars per row = 40 cars. You would probably fit less, as you would need some sort of cross path to link the three parking rows together. This was a bit sloppy math and doesn't take into account any local building codes or regulations that you may encounter. Page 4 of this pdf may provide you with more information on how to optimize your lot size and layout. http://www.apai.net/apai2003/designguide_0605/designguide/Chapter_5B.pdf