Market Size (Frost & Sullivan)

A good background on the importance of market sizing and high-level description of three approaches.  The article is geared more towards established businesses rather than startups.

How to Size a Market – Part I (MarketingProfs)

Discussest the issue from an Internet startup perspective.  Topics include the “primary and secondary demand” and the “chain ratio method”.  There is a Part II, but it requires an account.

How to estimate market size (Lightspeed Venture Partners)

Also from the Internet startup perspective. Focuses on the concept of “Total Addressable Market size (TAM)”. Gives an example using a top-down approach.

When, Why, and How to Calculate Potential Market (SBA.gov)

“Start with a large Number and narrow it down”. This is a common theme among these articles, though none of tell you much about how you get the large number to start with or how you can be sure you’re narrowing sufficiently.