PF21.3 fits standard desktop LCD monitors with a diagonally measured 21.29" viewable screen; actual filter dimensions are12 3/4" high x 17" wide. Screen data is visible only to persons directly in front of the monitor. 3M privacy technology darkens on-screen data when viewed from the side. Keeps your electronic information confidential, making it excellent for use in high traffic areas. Provides 1.5 times more effective privacy than competitive models. Helps protect your fragile LCD screen from damage. Filter is reversible. Choose matte side for anti-glare or glossy side for increased clarity.