Glossary
Eye level
The height at which the top of a monitor should sit relative to your eyes, roughly at or just below eye height.
Eye level, in a desk setup, describes where the top edge of your monitor should land relative to your eyes when sitting in your normal working posture. As a starting point, the top of the screen sits at or just slightly below eye height, with the whole display positioned about an arm's length away from your face.
Getting this wrong in either direction changes how your neck sits for hours at a time. A screen mounted too high tips the head back and strains the upper neck, while a screen sitting too low, a common problem with laptops used flat on a desk, pulls the head and shoulders forward into a hunch. A monitor arm or a simple monitor riser is usually the easiest way to fix either problem without replacing furniture.
People with bifocal or progressive lenses sometimes need the screen a little lower than this general rule, since they view text through the lower part of the lens. Multi-monitor setups add another wrinkle, since the primary screen used most of the time should get priority for correct eye level, with secondary screens angled toward it rather than treated as equally important.