Hi Neerav,
If measuring size of opportunity is so easy as feeding data like growth rate, discount rate to excel sheet, and getting a value, every single value investor would have been using it. The problem is that it is not easy to deduce, not easy to quantifiable, and not so easy to verify quickly.
Scuttlebutt can be an easy way to find size of opportunity. But again, just doing scuttlebutt cant give you the complete idea.
To feel the size of opportunity, one need to develop bird-eye/macro view of the economy. Which in turns requires hell a lot of reading, developing a complete different set of mental model.
I shall give you one single example : In the book " Making the Modern World: Materials and Dematerialization by Vaclav Smil" (which I am yet to read) The author has shown how China has consumed more cements in 5-10yrs, which USA consumed in last 80-100yrs. So, you get a feel how much cement would be needed by India, if it wishes to be like China of 2014 in say next 10-15yrs.
Another alternative can be what Donald calls “doing Phd in the stock”. You need to study all competitor/macro for the stock, and than you will have the gauge of “oppurtunity size”. But again, you cant choose 100s of stocks, dozen of sectors to do a Phd type research. It will be a too much effort exercise.