[thelist] How do you estimate time for any given project?

[Rob Smith]

Hello,

This question has once again passed through my office: How do you estimate
time for any given project? I would like to siphon your thoughts, ideas, or
other methods you use to get an estimate.

For example, I was tasked just recently to demo the possibility of a Web
Based Inventory Management System. Some of you where involved with this
(i.e. "Item A Item A Item A")

I managed to churn out the demo in about 3 days (12 actual work hours). I
was asked to write up a proposal to convert the real live thing to a working
secure scalable model for future interactions. I quoted around 100 man hours
with the help of one other colleague. 

The catch is I've never really done anything like this, so I have no clue
about how much to estimate. 

TIA,

Rob.Smith