In general the appropriate size will allow you to sit about 30" back from the screen with your eye level above the top of the monitor with a 30-degree downward gaze angle. Monitors that are bigger than you need, will usually sit too high on a desk. This forces our eyes to look up at them causing additional near viewing stress. Too small of a screen will force us closer to the monitor also adding to near viewing stress. A 15" or 17" monitor is usually the best size for most of us.

Monitor size is measured by the distance from one corner of the screen's viewable area to the diagonally opposite corner. With CRTs, the number is generally about an inch greater than the actual area. The real number is included in the specs. For example, you might see a 17" monitor state 16.1" viewable. With flat panel monitors, the screen size specification is actually its real size.

What matters is monitor resolution, not monitor size. In the Computer World, the screens usually take the size of 14", 15", 17", and 19" . There are 3 main screen resolutions: 640x480, 800x600, 1024x768 pixels. Usually 14-15" computers take on a 800x600 resolution, and larger screens use higher resolution, but this is NOT always the case. Some old 14" monitor can display up to 1024x768 pixels.

The monitor resolution or number of pixels in the viewing window affects the way it appears. Images and text have their dimensions ultimately specified in terms of pixels regardless of what’s being used to view them. The greater the number of pixels, the finer the resolution. An image on a monitor with a resolution of 1024 by 768 pixels will generally look better and be sharper than an image on a monitor with a resolution of 800 by 600 pixels or 640 x 480 pixels.

Resolution refers to the number of individual dots of color, known as pixels, contained on a display. Resolution is expressed by identifying the number of pixels on the horizontal axis (rows) and the number on the vertical axis (columns), such as 800x600. Resolution is affected by a number of factors, including the size of the screen.