TVsizeMatters  is a web-based application like no other I have seen before, and you won’t realize its worth till it’s time for you to buy a new TV.
TvsizeMatters lets a user upload a picture of any wall where a TV would be installed and lets him/her see how big or small different screen sizes will look on that wall.
For an ambitious idea, this works pretty well. For accuracy’s sake, you can use the ‘set the scale’ feature. When using this, you draw a line on the picture of the wall and enter its real-life length in the box provided.
For example, if you want to install the TV above the fireplace, then you can simply draw a line as long as the length of the fireplace and enter its real life length. Using this piece of information, the application figures out the dimensions of your wall and accordingly adjusts the variable TV screen sizes.
I highly recommend this before you buy a TV, especially if the room you’re installing the TV in is cramped or has a very busy wall. Give this webapp  a spin before you buy your next TV.