Determining Number of Apartments Calculator?

[Chad Jarrah]

Hello builders of BiggerPockets! This is a very vague and generalized question. Currently looking for a ballpark answer. Is there a rough way of determining the number of apartment units that can fit in a building while accounting for space loss due to walls, hallways and staircases?

There are a ton of variables like considering parking, allowable zoning requirements, etc, but just looking for an idea using this example:

20,000sqft building, each apartment being 900sqft.

Thanks!