How to Measure the Inches on a Computer Monitor

By Dan Stone

Updated August 23, 2017

Computer monitors are measured diagonally.
i Ryan McVay/Photodisc/Getty Images

Computer monitors are measured in the same way that television screens, smartphone screens and tablet screens are: diagonally. However, the diagonal measurement doesn't necessarily mean that one monitor is larger than another because the screen size measurement doesn't take into account the aspect ratio, which alters the total screen size. Monitors are commonly measured in inches using a tape measure or a yard stick.

Diagonal Screen Measurement

You can measure a computer monitor by measuring the distance between opposite corners on the viewable area of the screen. If you put each end of the measuring tool in the corner, you can get the screen's official size. However, if measuring corner to corner may be difficult to line up on a larger screen or you just don't want to get fingerprints on the monitor, you can alternatively use the Pythagorean Theorem to measure the screen size. Add the square of the screen's height and length measurements together, then determine the square root of the sum. The answer is the screen's size in inches.

Don't Count the Bevel

With older CRT monitors there is a discrepancy in how you should measure the size of the screen. Sometimes the measurement is provided by giving the visible area, but other times the size is determined including the bevel that borders the screen. The space including the bevel makes sense if you're trying to physically fit the screen in a confined location, but it doesn't work as well when describing viewable space. Flatscreen LCD monitor measurements do not include the bevel in the screen size: this is a problem of the past associated with CRT monitors. If you're measuring a CRT monitor, it's safe to measure the screen with and without the bevel.

Lining up the Measurement

You can measure a computer monitor with a tape measure. Turn the screen off before measuring the monitor as applying pressure can disrupt or cause minor damage to the screen when it's on. Line up the "0" measurement with one corner of the monitor and extend the tape measure across the screen to the opposite corner. The distance between the two corner dots is the screen's measurement in inches.

Aspect Ratio Relevance

The screen's aspect ratio measures how tall it is versus how long it is. While HDTV screens have a 16:9 ratio, computer monitors can come in 5:3 and 16:10 in addition to 16:9. The diagonal measurement system doesn't work well when comparing screen sizes across different aspect ratios because the aspect ratio changes the total screen area in relation to the diagonal measurement. The practice of measuring electronic display screens diagonally dates back to the television and CRT era where all screens used the 4:3 aspect ratio. To compare screen size between monitors with different aspect ratio, measure the screen area by multiplying the height by the screen length.