Flat panel TVs are measured like any other television. Their ideal viewing distance -- just as crucial as screen size -- is similar to other high definition TVs. Knowing how to properly measure a TV screen enables you to make the wisest purchasing decision for your tastes and the space available to you.
Measuring your Screen
Measure your television screen diagonally. Start at the upper-left corner and measure down to the lower-right corner. If you wind up with 40 inches, you've got a 40-inch TV.
The distance from which you view your TV is just as important as the size -- and changes depending on the size. According to Toshiba, the industry standard for determining optimal viewing distance requires some math. Multiply your screen's size by 1.2, then by 1.9. This gives you a range of optimal viewing in inches. Divide each result by 12 to convert your inches to feet. For a 40-inch TV, 40 multiplied by 1.2 and 1.9 gives you 48 and 76 inches. Dividing those figures by 12, the optimal viewing distance for a 40-inch television lies between four and 6.3 feet, depending on personal preference.
Viewing distance is important because poor placement can negatively impact your viewing experience. Sitting too close, you may be able to see the screen's pixels. Sitting too far means you may miss out on some picture detail.