Computer monitor sizes are based on the diagonal measurement of the screen. For example, a new LCD monitor advertised as being 32" in size is most likely 32" from upper right to lower left corner rather than 32" across or 32" tall. However, if you need to sell your current monitor or order a screen filter, measuring the screen yourself is the best approach for ensuring complete accuracy. Different monitor types may require specific filter sizes.
Measure the diagonal length of your screen from the top left corner to the bottom right corner. Measure only the screen; do not count the frame around the screen.
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Measure the height of the screen from top to bottom.
Measure the width of the screen from left to right. Once you have all three measurement values, you will be able to confidently order your screen filter or place your monitor up for sale.