Trade Volume

So I was looking over some of my favourite stocks, staring intently at the daily volume and thinking: "Is that a large volume ... or what? And large compared to what? Large compared to the average daily volume?" How about large compared to the number of outstanding shares? That's when I realized that I had no clue about how many shares trade compared to the total number of shares available for trading. As is my wont, I pulled up Excel and fiddled. I now got me a spreadsheet which gave this (for the S&P500): Click for an enlargement. So what did I learn? Not much, except that AIG trading is like 30% ... and that's large!