The switch to flat screen televisions means you can get sets that are much bigger -- yet often still lighter -- than their CRT predecessors. In most cases, this reduced weight means TV sets often don't need to come with a bulky built-in stand. You have many more options for choosing a tabletop or stand on which to place your TV. Having the right-sized stand can make viewing comfortable and keep your TV set stable.
You will find the width of most TV sets in the specifications posted on the manufacturer's website, or in the user's manual, which may be downloadable from the site. If this information isn't available, you will get a good estimate by working from the listed screen size, which refers to the diagonal measurement of the screen. Assuming you are buying a standard widescreen television, which has a 16:9 screen ratio, multiply the diagonal screen size by 0.87 to get the width of the screen.
In theory, your stand only needs to be the width of the base that comes with the television, the size of which may be available from the listed specifications or the instruction manual. It's best that the stand be at least the width of the television, which will be a few inches greater than the width of the screen. This will give you reassurance that you are unlikely to knock the screen off the stand. Ideally, the stand should be a few inches wider than the television set, as this will make it easier to reach around the back of the set to adjust cables.
For maximum comfort, the middle of your screen should be at or slightly below eye level from your viewing position. Calculate this height with a tape measure from your usual seated position. If you don't know the height of your TV screen, multiply the diagonal screen size by 0.49. Then take the height of your ideal viewing position and subtract half the height of your TV screen to get the middle of the screen, then subtract the height of the base that fits underneath the TV; this will give you the ideal height for your TV stand. You may not find the perfect-sized stand, but try to get one in the general area. If you have to choose between the screen being a little higher or a little lower than the ideal height, err towards the screen being a little lower.
Always check that your prospective stand is suitable for carrying the weight of your television. Most stands specifically designed for TV sets will list a maximum weight-bearing load. With flat-pack furniture, bear in mind that the maximum weight capacity may assume the stand has been put together perfectly and is therefore at full strength. So, when in doubt, buy a stand which has a comfortably greater load capacity than the weight of your TV.