The task is to make the box on the table/floor be in real dimensions, nowhere in the documentation did not find how to do this?
Ideally, there should be some scale or ruler, so that the dimensions of virtual objects are calculated from it.

The documentation says that all dimensions in A-Frame are in meters, but it’s all abstract.
Let’s say

The box will not be 4 meters long, it will be small, it will fit on a cell phone, you will not need to move your hand to see it out of sight.