How To: Make the scale/size of the map in the layout match a printed copy
Steps to make the size of the map elements on the screen, when zoomed to 100%, the same size as when printed.
ArcMap assumes a monitor size of 15 inches and bases the size of all map elements according to this. If your monitor is a different size, you can specify your display width and height in the ArcMap Advanced Settings Utility.
Quit ArcMap, if it is running.
Access the ArcMap Advanced Settings Utility.
A. Navigate to the Utilities folder under the ArcGIS installation directory; for example, C:\arcgis\arcexe81\Utilities.
B. Double-click AdvancedArcMapSettings.exe.
Click the Miscellaneous tab.
In the Monitor section, type your display width and height in millimeters. An easy way to find these values is to measure the width and height of a fully-maximized application, such as ArcMap.
Close the ArcMap Advanced Settings Utility.
The next time you use ArcMap, the size of the printed copy should more closely match the size of the layout display.