While TV size isn’t everything, as esoteric measurement standards say, screen size is one of the least intuitive. It’s a consideration to make whenever you buy a new TV, laptop, or PC monitor, and you’ve probably noticed that screens are always measured in inches and always diagonally. Although it will eventually become second nature to many (especially in the age of widescreen television, where width is the dominant dimension), the initial impulse is to assume that size refers to width, given that that’s how we measure other common objects, like furniture.
The problem with screens is the aspect ratio. Because they vary so widely, ranging from classic 4:3 to ultra-wide formats like 21:9, simply defining the width of a screen does not necessarily give an accurate indication of its overall size. Diagonal measurement solves this problem by providing a consistent metric that can be used to universally compare screen sizes, regardless of aspect ratio. While it doesn’t give a complete idea of a screen’s dimensions, it provides a simple shortcut for comparison between devices and can be useful in use cases such as determining if your TV is too small.
Origins and logic behind measuring screen diagonal
The other important consideration is that a diagonal measurement is the largest, so it’s a boon for manufacturers and marketers looking to inflate the perceived size of their products. That said, diagonal measurement dates back to the era of cathode ray tube (CRT) televisions. CRT displays were originally circular, so size was expressed as a measurement of the diameter of the display. As television sizes began to expand and move to square and rectangular formats, the diameter was gradually removed for a simple, single expression of screen size.
A diagonal measurement is both effective and inclusive. The diagonal of a rectangle is derived from the Pythagorean theorem, taking into account both height and width, so both dimensions are folded. It’s also much quicker to describe a screen as a single diagonal than having to clumsily spell out width and height, although spec sheets typically show a screen’s aspect ratio and resolution along with the raw size to add important context.
