Screen.AvailableWidth

From Xojo Documentation

Read-Only Property (As Integer )
IntegerValue = aScreen.AvailableWidth

Supported for all project types and targets.

The available width (in pixels) of the screen, taking into account the taskbar if placed on the left or right of the specified screen. Use the Screen method to call AvailableWidth. For example, Screen(0).AvailableWidth returns the available width of the main screen.