# How to Calculate Pixels Per Inch

by Eric Fenton

When buying a monitor or a television, the number of pixels per inch is a good measure of the pixel size on the display. A pixel is the basic unit of the display screen's composition. If your display has very large pixels, you will need to be farther away from the screen to have a good view. On the other hand, if your display has very small pixels, you will need to be much closer to the screen to read small print. A good measure of this is the pixels per inch, or PPI, of your screen.

Collect the specifications of your particular screen. This must include the resolution of your screen and the diagonal length of your screen's viewable area. Note that this may differ slightly from the advertised screen size. For example, some 46-inch high-definition TVs actually have a diagonal of 45.9 inches. The exact viewable area of your screen will be in your user's manual.

Find the sum of the squares of the numbers of horizontal and vertical lines. For example, if you have a 23-inch screen with a resolution of 1920 by 1,080, calculate (1,920^2 + 1,080^2), which is 4,852,800.

Take the square root of your result from Step 2. For a 23-inch 1,920-by-1,080 screen, this value is approximately 2,203. This is the total number of pixels along the diagonal of your monitor.

Divide the number of pixels along the diagonal of your monitor by the diagonal length of your monitor. For the example monitor, you would divide 2,203 by 23, which is approximately 95.8. This is the number of pixels per inch of your monitor.