With the advent of larger TV at lower prices (especially around the winter holiday season), a common question arises -- what is the correct size TV for a given sized room/space?
CNET has a good article on the subject, which explains in gory detail how big a TV you should buy.
Overall, it details how to select the right TV size for a given room, based on mathematical calculations - using the seating distance from the TV & a percentage of a human's field of vision.
For those who want to skip right to the details, here are the formulas.
An angle of 40 degrees creates an immersive cinematic experience. For this, simply multiply your seating distance (in inches or centimeters) by 0.84. This gets you the recommended screen diagonal. So given a 9-foot seating distance, a TV around 90 inches diagonal would work.
An angle of 30 degrees creates a standard viewing experience, which is obviously quite a bit smaller. For this, simply multiply your seating distance by 0.625. So given the same 9-foot seating distance, that means a TV around 68 inches diagonal would work.
CNET further recommended no closer than 1.5 times the screen diagonal, or 0.667 times the seating distance. This allows for a slightly larger TV, for an optimal viewing experience. This number allows you to calculate a 'maximum' screen size, for most viewing situations without going overboard. So given our 9-foot seating distance, a 'maximum' screen size of 72 inches (or say a slightly smaller 70 inches) diagonal would be optimal for the space.