Instructions provided describe how to create a custom page size for multiple page print tiles, based on the the extent and scale of the map.
ArcMap does not have the capability to adjust a page size to accommodate a specific extent/scale that is set. The following is a workflow to find an appropriate page size to fit a specific extent and scale set for the purpose of printing tiles for a multiple page display.
Alternatively, the Minimum Bounding Geometry tool can be used to generate an envelope with the length and width measurements. Use the Envelope option and check the box to 'Add geometry characteristics...'. If this method is used, be sure to round the resulting value measurements up.
Minimum Bounding Geometry tool
Measured length = 572 ft.
Rounded length = 600 ft.
Measured width = 381 ft.
Rounded width = 400 ft.
desired scale = 1:60
600 / 60 = 10 ft.
400 / 60 = 6.67 ft.
Scaled length: 10 * 12 = 120 inches
Scaled width: 6.67 * 12 = 80 inches
Page and Print Setup Window
It is highly recommended to turn off all unnecessary layers, imagery, and services while modifying the map elements to improve drawing performance while making these adjustments.