We get quite a few questions about marketcap- We provide that data going back to 2008 for US securities. If you want to access that data through the API, here is a tutorial:
If you want to work with Excel, here is the tutorial for the Excel add in:
In the API, a historical marketcap call would look like this:
To get the current marketcap, you would do this:
In Excel, historical marketcap:
=intriniohistoricaldata("AAPL", "marketcap", 2, "2009-01-01", "2011-01-01")
Or, the most recent marketcap in excel:
The blog provides a lot more detail, including this template example.