Diagram comparing various typical screen sizes by width, height, diagonal, area and aspect ratio.

On two-dimensional display devices such as computer monitors and television sets, the display size (or viewable image size or VIS) is the actual amount of screen space that is available to display a picture, video or working space, without obstruction from the case or other aspects of the unit's design. The viewable image size (often measured in inches or millimeters) is sometimes called the physical image size, to distinguish it from the "logical image size" (display resolution, measured in pixels) of various computer display standards.

The size of an approximately rectangular display is usually given by monitor manufacturers as the distance between two opposite screen corners, that is, the diagonal of the rectangle. This method of measurement is inherited from the method used for the first generation of CRT television, when picture tubes with circular faces were in common use. Being circular, only their diameter was needed to describe their size. Since these circular tubes were used to display rectangular images, the diagonal measurement of the rectangle was equivalent to the diameter of the tube's face. This method continued even when cathode ray tubes were manufactured as rounded rectangles; it had the advantage of being a single number specifying the size, and was not confusing when the aspect ratio was universally 4:3.

A problematic practice was the use of the size of a monitor's imaging element, rather than the size of its viewable image, when describing its size in publicity and advertising materials. On CRT displays a substantial portion of the CRT's screen is concealed behind the case's bezel or shroud in order to hide areas outside the monitor's "safe area" due to overscan. These practices were seen as deceptive, and widespread consumer objection and lawsuits eventually forced most manufacturers to instead measure viewable size^{[citation needed]}. On cathode ray tube monitors, VIS differs noticeably from the full tube size, which is generally about 25 mm (1 in) larger.

Liquid crystal displays use 100% of their surface to display, thus the VIS is the actual size presented to the viewer.

In the U.S., manufacturers and retailers are allowed to list the tube size, which is misleading and confusing to many customers, especially when comparing both CRT and LCD models together. In many other countries, this practice is prohibited by consumer-protection laws.

Measurements and units[link]

The practice of measuring display devices by the diagonal is a remnant from the time when cathode ray tubes were used, which basically created circular projections, and any rectangular area derived thereof had a diagonal equal to the circle diameter.

The main measurements for display devices are:

• Width and height
• Total area
• The diagonal, usually measured in inches. The diagonal measurement of a display as the actual viewable area is also dependent on the aspect ratio of the display. For a display device of the same area, the diagonal achieves a larger value in a widescreen than compared to a more square screen. There is a risk of manufacturers making displays wider than what is actually most convenient in order to make the diagonal achieve a larger value.

Conversion equations[link]

The width and height can be calculated from the diagonal as follows:

Failed to parse (Missing texvc executable; please see math/README to configure.): height=\sqrt{\frac{D^2 \times H^2}{W^2+H^2}}

Failed to parse (Missing texvc executable; please see math/README to configure.): width=\frac{W}{H} \times height

, where:

• D is the diagonal
• W and H are taken from the aspect ratio as W:H, or, alternatively, by the screen resolution given by rows of pixels (assuming square-shaped pixels).

Conversion charts[link]

These are charts of some common sizes of LCDs with varying aspect ratios and their actual viewable area.

See Also[link]

• Display resolution