Fixed Grid and fixed size

In Blender, we need a way to fix the grid so that zooming out does not change the display of the grid. We also need a way to be able to enter a fixed size. For instance I might want to work in a fixed grid size of 30cm which is close to an imperial foot. For working with assets to Unreal Engine, its important to work in set grid sizes for the purposes of modularity and snapping.
I propose that in the over lays panel, there be a checkbox for 'fixed grid' and then a numeric field for a set grid size.