I work for a company that will be deploying VoIP, Data, and soon to be
Video to USA residental apartment complexes. But we have no idea how
much bandwidth is needed. Is there a equation, calculator, or a
general rule to say that each user will need to have so much amount of
bandwidth? Seeing that some will be average web surfers while others
will be gamers and watch streaming video im sure.

Currently I am just looking at getting a fractional DS3 and then
watching the MRTG graphs to make sure they dont start "clipping".

The answer provided needs to also be scalable. So it could be used for
an apartment complex of 50 people all the way up to 1000 people.

Howdy cryption-ga,

You are trying to take an engineering approach to a policy problem.  You
need to set a limit to the use by your end users and then configure your
system(s) to manage that limit.

If you do not take that approach, the formula for usage will soon become
a range from (easily) 100G a month to 1T a month per unit as people find
out there is "unlimited" bandwidth available.

No matter what you provide, there will always be some "clipping" of the
bandwidth by "abusers" of the system, unless you put into place some kind
of metering and bandwidth limiting system, which would also provide some
type of user feedback system (a web page with usage statistics for the end
user) so people could monitor their own usage.

Looking Forward, denco-ga - Google Answers Researcher

Correct people's amount of bandwidth will be capped at the amount of
the "package" that they purchase. But i was hoping that there would be
some rule. since there will be some older people that may just surf
and do email. While others are gamers.

I think that if you allocated 3 mbp to each person in a 100 apt
complex that it would be unlikely that you would need a 300mbp pipe.

While this probably doesn't answer your question, it may help you a
bit -- and if not, hopefully you'll at least find it an interesting
read:

http://www.ct-magazine.com/archives/ct/0402/bandwidth.html