You need to set the cube size. On average, it is between 2100 to 2400. If you change it, it will stay to what was last used. If you have cube numbers, it uses them to calculate against what the iPad App has for a cube size and subtracts that value when an item is added to a container order.
In the upper right hand corner of the app, there is a cube size box in the container order section.
Select the truck icon container button first.
Headers used in the configuration of Containers: Cubes, Source and ContainerMinQty. More information on Headers