Screen size is a diagonal measurement of the lit portion of the panel, expressed in inches. Monitors, laptops, tablets, phones, and televisions all follow the same convention. It is the reason a 15.6-inch laptop and a 15.6-inch monitor have screens of the same size, even though the machines around them look nothing alike.
Computer screens are measured diagonally, from one corner of the visible display area to the opposite corner, and the result is given in inches. A 27-inch monitor is therefore 27 inches corner to corner, not 27 inches across. The measurement covers the active display area only. Bezels, the plastic housing, the stand, and a laptop lid are all excluded from the figure.
That single number leaves a lot unsaid, though. Two screens with an identical diagonal can differ noticeably in width, height, and total usable area. This article explains how the measurement works, how to take it yourself, and why the aspect ratio matters just as much as the inches.
Why the diagonal instead of the width The convention dates back to early television sets, which used round cathode ray tubes. The diagonal was the most practical way to describe a circular picture area, and the practice carried over to rectangular screens and then to computer monitors.
There is a practical reason the convention survived. The diagonal compresses two dimensions into one number, which makes displays straightforward to compare on a shelf or a specification sheet. It also produces a larger, more appealing figure than either the width or the height alone.
The tradeoff is that the diagonal alone cannot tell you the actual shape of the panel. For that you need the aspect ratio.
Why inches, when most of the world uses metric Screen sizes are quoted in inches almost everywhere on earth, including in countries that have used the metric system for over a century. Four separate forces keep that convention in place.
The category was born in an imperial market. Television manufacturing was dominated by American firms when the sizing convention was established, and the United States measured in inches. Panel production later moved to Japan, South Korea, Taiwan, and China, but the vocabulary traveled with the product rather than being rewritten at each stop.
One global supply chain needs one language. Panel manufacturers sell the same glass to every brand in every market simultaneously. Maintaining a single sizing standard is considerably cheaper than maintaining several, and the industry settled on the one it already had.
Model numbers depend on it. Manufacturers encode the diagonal directly into product names, so an Acer monitor model beginning XB273 signals a 27-inch panel and a laptop model beginning SF16 signals a 16-inch machine. Switching units would break naming conventions, catalogs, and spare-part systems worldwide.
Inches produce tidier numbers. Common sizes land on memorable whole figures such as 24, 27, and 32. The metric equivalents are 61.0 cm, 68.6 cm, and 81.3 cm, which are harder to recall and harder to compare on a shelf.
What the law actually requires European rules do not ban the inch. Directive 80/181/EEC, in force since October 1981, requires metric units to appear and to predominate, but it permits supplementary indications in other units alongside them. That permission was originally due to expire, and was later extended for an unlimited period.
The practical result is the labeling you see across European retail. A monitor is listed as 68.6 cm with 27 inches shown next to it, and the model number still says 27. Both figures describe exactly the same panel.
Converting between the two One inch equals 2.54 centimeters exactly, so the conversion is straightforward.
Screen size
Metric equivalent
13.3 inches
33.8 cm
14 inches
35.6 cm
15.6 inches
39.6 cm
16 inches
40.6 cm
24 inches
61.0 cm
27 inches
68.6 cm
32 inches
81.3 cm
34 inches
86.4 cm
How to measure a monitor yourself
You need a tape measure or a ruler, and the entire process takes less than a minute.
Turn the monitor on briefly so you can see exactly where the lit area starts and stops. Place the end of the tape at the bottom left corner of the visible image. Stretch it diagonally to the top right corner of the visible image. Read the measurement in inches and round to one decimal place. Do not include the bezel, the frame, or the stand. Measuring the outer edge of the housing will overstate the size by an inch or more on older displays with thick borders.
Manufacturers also round their figures. A screen advertised as 27 inches often measures 27.0 inches exactly, but a 15.6-inch laptop panel really is 15.6 rather than 16.
How to measure a laptop screen The method is identical to the procedure above. Open the lid, measure the visible display area diagonally from corner to corner, and ignore everything outside it.
The common mistake here is measuring the lid instead of the panel. A laptop lid is always larger than the screen it protects, so that figure will not match the advertised size.
It is also worth knowing that laptop screen size does not describe the footprint of the machine. A 16-inch laptop is approximately 14 inches wide, because the diagonal always exceeds the width on a rectangular panel.
Aspect ratio changes what the inches actually mean Aspect ratio is the proportion of width to height. It determines the shape of the rectangle that the diagonal is drawn across.
Three ratios cover most computer screens:
16:9 is the standard widescreen format used by most monitors and many laptops16:10 is slightly taller and increasingly common on laptops and productivity monitors21:9 and 32:9 are ultrawide formats aimed at multitasking and immersive gamingHere is why this matters. A 16:10 screen has approximately 5% more surface area than a 16:9 screen of the same diagonal, because the extra height adds more area than the lost width removes. The spec sheet shows the same number of inches, but you get more room to work.
Actual width and height by screen size The table below converts common diagonal sizes into real dimensions. Figures are for the display area only and are rounded to the nearest tenth of an inch.
Screen size
Aspect ratio
Width
Height
13.3-inch laptop
16:9
11.6 in
6.5 in
14-inch laptop
16:10
11.9 in
7.4 in
15.6-inch laptop
16:9
13.6 in
7.6 in
16-inch laptop
16:10
13.6 in
8.5 in
24-inch monitor
16:9
20.9 in
11.8 in
27-inch monitor
16:9
23.5 in
13.2 in
32-inch monitor
16:9
27.9 in
15.7 in
34-inch monitor
21:9
31.3 in
13.4 in
Two comparisons are particularly instructive.
A 16-inch 16:10 laptop panel is the same width as a 15.6-inch 16:9 panel, but it is nearly an inch taller. The machines occupy similar desk space while one shows considerably more of a document or timeline.
A 34-inch ultrawide is barely taller than a 27-inch monitor. It is far wider instead, which is why ultrawides suit side-by-side windows rather than taller ones.
Working out the numbers yourself If you know the diagonal and the aspect ratio, you can calculate the width and height directly.
Divide the diagonal by the square root of the sum of the squared ratio numbers, then multiply that result by each ratio number in turn.
For a 27-inch 16:9 monitor:
Square the ratio numbers: 16 x 16 = 256, and 9 x 9 = 81 Add them together: 337 Take the square root: approximately 18.36 Divide the diagonal: 27 divided by 18.36 = approximately 1.47 Multiply out: 1.47 x 16 = 23.5 inches wide, and 1.47 x 9 = 13.2 inches tall How curved screens are measured Curved monitors use the same diagonal figure, taken as a straight line rather than traced along the curve.
The curvature itself is quoted separately as a radius, written as a number followed by the letter R. A 1000R panel is more sharply curved than an 1800R panel, because the number describes the radius of the circle the curve would form, measured in millimeters. Lower means tighter.
Curvature is a comfort and immersion specification. It does not change how the screen size is measured.
Where resolution and pixel density fit in Screen size describes physical dimensions. Resolution describes how many pixels fill those dimensions. Neither one tells you how sharp a display looks on its own.
The figure that combines them is pixel density, measured in pixels per inch, or PPI. You calculate it by dividing the diagonal pixel count by the diagonal size in inches.
A 27-inch monitor at 4K works out to approximately 163 PPI. The same 4K resolution stretched across a 32-inch panel drops to approximately 138 PPI. Identical pixel counts, different sharpness, purely because of the physical size.
This is why the inches on a specification sheet only make sense alongside the resolution. Buying a larger screen without raising the resolution makes the image less sharp, not more.
How to find your screen size without measuring Three approaches are available when a tape measure is unavailable.
Check the model number. Most manufacturers encode the size into it. An Acer monitor model beginning XB273 is a 27-inch panel, and a laptop model beginning SF16 is a 16-inch machine.
Look at the label. Monitors carry a sticker on the rear housing listing the model and serial number, and laptops usually have the same information on the underside.
Search the specification sheet. Enter the model number on the manufacturer support site to pull up the full panel specification, including size, resolution, and refresh rate.
Note that Windows display settings will show you the resolution and refresh rate, but not the physical size of the panel.
Acer screens worth a look
Once you understand the measurement convention, choosing a screen becomes a question of matching the diagonal, the aspect ratio, and the resolution to the work you do.
For desktop use, the Predator XB3 range includes a 5k monitor option built around a 5120 x 2880 panel in the standard 16:9 format. Because pixel density depends on physical size, a resolution that high keeps the image sharp even on a large diagonal. The series also pairs high resolution with NVIDIA G-SYNC Pulsar for motion clarity, DisplayHDR 600 for contrast, and factory color calibration rated at Delta E under 1. Specifications vary by model, so verify the particular model you are buying.
For portable use, the aspect ratio argument above applies directly. The Acer Swift 16 AI is a 16 inch touch screen laptop with a 16:10 panel running 2880 x 1800, which is the taller format that gains approximately 5% more display area than 16:9 at the same diagonal. That extra vertical space shows more of a page, a timeline, or a code file without any scrolling. The panel covers 100% of the DCI-P3 gamut with Delta E under 2, refreshes at up to 120 Hz, and carries VESA DisplayHDR True Black 500 certification. Stylus support with MPP 2.5 tilt makes the touch layer useful for sketching and markup rather than just tapping.
The two work well together. The Swift 16 AI has HDMI 2.1 with output up to 8K plus two Thunderbolt 4 ports, so it can drive a large external display without a separate dock. If you want to compare screen sizes across other thin and light configurations, the broader premium laptop lineup covers a range of diagonals and panel technologies.
Frequently asked questions How are computer screens measured? Computer screens are measured diagonally, from one corner of the visible display area to the opposite corner, with the result given in inches. The measurement covers the lit panel only and excludes the bezel, the housing, the stand, and any laptop lid.
Is a 27-inch monitor 27 inches wide? No. A 27-inch monitor is 27 inches measured diagonally. In the standard 16:9 aspect ratio, the display area is approximately 23.5 inches wide and 13.2 inches tall.
How do you measure a laptop screen? Open the lid and measure the visible display area diagonally from the bottom left corner to the top right corner, then read the figure in inches. Do not measure the lid or the outer casing, because both are larger than the screen itself.
Does screen size include the bezel? No. The advertised screen size refers only to the active display area. Bezels, frames, and housing are excluded, which is why two monitors with the same stated size can have different overall dimensions.
Do 16:9 and 16:10 screens of the same size have the same area? No. A 16:10 screen has approximately 5% more display area than a 16:9 screen with the same diagonal measurement. The 16:10 panel is slightly narrower but noticeably taller, and the added height more than offsets the lost width.
How are curved monitors measured? Curved monitors are measured diagonally as a straight line, not along the curve of the panel. The curvature is listed separately as a radius value such as 1000R or 1800R, where a lower number indicates a tighter curve.
Why are screens measured in inches instead of centimeters? The convention began with the American television industry, and it persisted because panel manufacturing serves every market through a single global supply chain. Model numbers also encode the diagonal in inches. European rules require metric units to predominate on labeling, but they permit inch measurements to be shown alongside them, so both figures usually appear.
How many centimeters is a 27-inch monitor? A 27-inch monitor measures 68.58 cm diagonally, since one inch equals exactly 2.54 centimeters. Retailers in metric markets normally round this to 68.6 cm.
How can I find my screen size without measuring it? Check the model number, since most manufacturers encode the diagonal into it, or read the label on the rear of a monitor or the underside of a laptop. You can then enter that model number on the manufacturer support site to view the full panel specification.
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