Does anyone know how you can determine how many parking spaces can fit in a ground floor or underground parking garage? Assuming lot size is 10,000 sqft, 100x100. 

I think that the average space for a parking space is 350 sq ft. 

Parking lot spaces are 9 ft wide , lines are 18 ft long . Traffic isle is 20 ft wide ( or as close as possible) .   To get an accurate count you have to draw it out to scale . 

I have tried drawing it out to scale today. I used 90 degrees stalls, there are varying degrees of course. I was more asking if there was free software or something else that could make it easier than just guessing or needing to hire a planner.

There is a specific computer program that does this calc for you. I think it's part of the auto cad suite but not sure. For zoning purposes you usually need to hire a planner.