Source: http://lifehacker.com/5829786/tv-size-matters-lets-you-try-new-tvs-on-for-size-before-you-buy
When buying a new HDTV, the first thing you should settle on is where in your room the set should go. Webapp TV Size Matters can help: upload a photo of the room where the TV will go, set a standard scale, and the service lets you try different-sized TVs for size to see how they fit.
The webapp gets a feel for scale by asking you to draw a line on your uploaded photo and tell it how large that line is in real life. From there, the service understands how large or small to display different sized sets on your wall or entertainment center, so you can see how they'll realistically look when they're in your home.
For many people, there's only one logical place in their room for their TV to go, but if you have the option of wall-mounting or you want to see whether your space can handle a larger display, TV Size Matters is worth a look.
You can reach Alan Henry, the author of this post, at alan@lifehacker.com, or better yet, follow him on Twitter.