What is the average size of a tv?

>> 50" inch (127cm)

That answer is complete and utter nonsense, with no evidence to support it. I have seen multiple statements like this, but you should remember that they are probably motivated by people who have a vested interest in convincing you that you need a larger TV to enjoy their mediocre programming. Evidence from video enthusiast sources are also misleading, since they represent a group of people who are more interested in spending large amounts on a large screen.

There are also two possible numbers to report:

1. the average size of newly purchased television sets. According to "Modeling of price effects for the adoption of LCD TV", published in August 2009, (http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&arnumber=5261817&isnumber=5261733), the average size telvision set being sold was still a 32". This number may be a year old, but I would be very surprised if the average size was bigger than 37" at this time, because the price differential between a 32" and larger sets is still quite large.
2. the average size of television sets that are in use. Television sets tend to last a long time, so this number is probably smaller than the former.

Recent technological trends have made larger sets more affordable, but price trends have still maintained a large price gap between larger sets and the prevalent 32" model.