How do you calculate the number of parking spaces need for an office complex?

How do you calculate the number of parking spaces need for an office complex?
You need first to know the ratio ofvehicles per capita of your city. Then you'll need to know what kind of people will work in this complex. You know, one hundred managers or lawyers will surely have (and use) more cars than one hundred call center operators. The third data to get is the availability of public transportation around this complex, if it is too difficult to get by train and/or bus, people will surely use more cars (or bicycles depends in witch country you're in). That's all for the employees of the complex. The next step is to calculate the flow of people visiting this complex, to know what kind of people and so on.

Usually in bigger cities the parking is paid (and expensive) and office buildings/complexes have far more parking spaces than the building (or buildings) alone would need, just to make a profit with the lack of parking spaces in the neighborhood.