Display size

For the number of pixels measured vertically and horizontally per screen, see Display resolution.

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 TV and 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. In the US, when virtually all TV tubes were 4:3, the size of the screen was given as the diagonal with a V following it. In Japan and other markets, the size of the outer diameter of the tube was given. What was a 27V in the US would be a 28" in Japan. However the V terminology was frequently dropped in US advertising referring to a 27V as a 27". This was not misleading for the consumer as the seller had to give the actual screen size by law. Liquid crystal displays use 100% of their surface to display, thus the VIS is the actual size presented to the viewer.

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).

When the common aspect ratio went from 4:3 to 16:9, the new widescreens were labeled with a W. A screen that is approximately the same height as a 27V would be a 32W. Recently Vizio and other US TV manufacturers have introduced even wider screens with a 21:9 aspect ratio in order to match aspect ratios used in cinemas. In order to gauge the relative sizes of these new screens, the screen aspect must be considered. Indeed, in a commercial market where multiple aspect ratios are being sold, it will always take two numbers to describe the screen size, some combination of diagonal, aspect ratio, height or width.

Set sizes are frequently given as a "class" as screens from different manufacturers will have slight differences in size. However the "class" should be within 1/2" of the actual size. The reasons for the different sizes within a class stem from differences in the manufacturers' equipment. LCDs are cookie-cut from one large piece of glass. As manufacturers move from one size to another, newer larger sizes must fit on the same size glass, though with fewer displays being cut from it. Some sizes fit well and maximize glass utilization, other sizes fit more poorly and waste glass. As an example, in some cases, increasing the screen size by even 0.1" can cause an LCD manufacturer to go from 12 screens fitting on their glass sheet to 9. This would make them uncompetitive with other screen makers.

Ideal Screen Size

The TV image is composed of many lines of pixels. Ideally, the TV watcher sits far enough away from the screen that the individual lines merge into one solid image. The watcher may sit even farther away and still see a good picture, but it will be a smaller portion of their visual field. The resolution of the human eye (with 20/20 vision) is about one minute of arc. For full HDTV resolution, this one minute of arc implies that the TV watcher should sit 4 times the height of the screen away. So the ideal set size may be determined from the chart below by measuring the distance from where the watcher would sit to the screen in inches, dividing that by 4, and comparing with the screen heights below. If the user is replacing a standard definition TV with an HDTV this implies that the best visual experience will be with a set that is twice as tall as the standard definition set. As the average size LCD TV being sold is now 38", which is only about 15% taller than their old 27V, this means that most consumers buy HDTV sets that are smaller than what they could utilize. Of course, in addition to screen size, budget sizes must be considered as well.

Measurements and units

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

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

$height=D \times \sqrt{\frac{H^2}{W^2+H^2}}$

$width=\frac{W}{H} \times height$

, 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

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

Width, height and viewable area from diagonal measurement and aspect ratio, rounded to centimetres

Diagonal			5:4				4:3				16:10				5:3				16:9
(in)	(cm)		w (cm)	h (cm)	A (cm²)		w (cm)	h (cm)	A (cm²)		w (cm)	h (cm)	A (cm²)		w (cm)	h (cm)	A (cm²)		w (cm)	h (cm)	A (cm²)
3.5	9		7	6	39		7	5	38		8	5	36		8	5	35		8	4	34
3.7	9		7	6	43		8	6	42		8	5	40		8	5	39		8	5	38
4	10		8	6	50		8	6	50		9	5	46		9	5	46		9	5	44
4.3	11		9	7	58		9	7	57		9	6	54		9	6	53		10	5	51
5	13		10	8	79		10	8	77		11	7	72		11	7	71		11	6	69
7	18		14	11	154		14	11	152		15	9	142		15	9	139		15	9	135
10	25		20	16	315		20	15	310		22	13	290		22	13	285		22	12	276
11.6	29		23	18	423		24	18	417		25	16	390		25	15	383		26	14	371
13.3	34		26	21	557		27	20	548		29	18	513		29	17	503		29	17	488
14	36		28	22	617		28	21	607		30	19	568		30	18	558		31	17	540
15	38		30	24	708		30	23	697		32	20	652		33	20	640		33	19	620
15.4	39		31	24	746		31	23	734		33	21	688		34	20	675		34	19	654
17	43		34	27	910		35	26	895		37	23	838		37	22	823		38	21	797
18.5	47		37	29	1077		38	28	1060		40	25	992		40	24	974		41	23	944
19	48		38	30	1136		39	29	1118		41	26	1047		41	25	1028		42	24	995
20	51		40	32	1259		41	30	1239		43	27	1160		44	26	1139		44	25	1103
21	53		42	33	1388		43	32	1366		45	28	1279		46	27	1255		46	26	1216
22	56		44	35	1523		45	34	1499		47	30	1403		48	29	1378		49	27	1334
23	58		46	36	1665		47	35	1638		50	31	1534		50	30	1506		51	29	1458
24	61		48	38	1813		49	37	1784		52	32	1670		52	31	1639		53	30	1588
25	64		50	40	1967		51	38	1935		54	34	1812		54	33	1779		55	31	1723
26	66		52	41	2127		53	40	2093		56	35	1960		57	34	1924		58	32	1864
27	69		54	43	2294		55	41	2258		58	36	2114		59	35	2075		60	34	2010
28	71		56	44	2467		57	43	2428		60	38	2273		61	37	2231		62	35	2161
29	74		58	46	2647		59	44	2604		62	39	2439		63	38	2394		64	36	2318
30	76		60	48	2832		61	46	2787		65	40	2610		65	39	2562		66	37	2481
31	79		61	49	3024		63	47	2976		67	42	2787		68	41	2735		69	39	2649
32	81		63	51	3223		65	49	3171		69	43	2969		70	42	2915		71	40	2823
37	94		73	59	4308		75	56	4239		80	50	3970		81	48	3897		82	46	3774
42	107		83	67	5552		85	64	5463		90	57	5115		91	55	5021		93	52	4863
50	127		99	79	7868		102	76	7742		108	67	7249		109	65	7116		111	62	6892
99	251		196	157	30845		201	151	30351		213	133	28419		216	129	27897		219	123	27019
102	259		202	162	32743		207	155	32219		220	137	30167		222	133	29613		226	127	28681
108	274		214	171	36708		219	165	36121		233	145	33821		235	141	33199		239	134	32155
111	282		220	176	38776		226	169	38155		239	149	35726		242	145	35069		246	138	33966

See also

• Display resolution