Both AR Kit and the All World platform use meters to determine the space a model occupies initially so its import to decide on a definitive scale for your work. If you are unsure, open a model of yours and check the world settings.
Maya for instance defaults to centimeters so you will need to go to the preferences and change the working units in settings to from centimeter to meter.
The grid will now reflect your new working unit of meters. You can now properly gauge the space your object will occupy upon oping in All World.
Scale accordingly if your object's opening scale is not not your liking for pieces meant to be shown indoors we recommend keeping your model under two meters.
*depending on your program you may need to freeze the transforms
Your mesh can now be exported for other steps.