What is the size of the default grid floor? I'm a total Blender beginner. I'm struggling with something regarding the default platform/floor that comes up when you first open blender.

Does anyone know the size of that default floor/grid/area that sits there before you, once you've just opened up the Blender programme? I.e. is it one mile long by one mile wide? Or one metre long by one metre wide? Etc?

The reason why I ask is because I used the shapes tool to draw a cube on the screen, whose size (actual "measurements", not merely "scaling") I made 10 MILLIMETRES long by 10 Millimetres wide by 10MM depth, but then it just seemed to disappear from the screen! When I re-sized its measurements to 10 METRES H. by 10 Metres W. by 10M D., then it did show up clearly, sitting on the floor/platform/area's base (not floating in the air, of course). Why would a large cube stay sitting in front of me on the screen, when a tiny cube vanishes into thin air? So, of course, I can't even see it or click on it to move it around any more.
Blender 2.79 or earlier
The X-Y grid that is visible in the viewport at all angles is 16x16 &quot;units&quot; large.

It is infinite if you are in any of the ortographic views: Top Numpad 7, Right Numpad 3 or Front Numpad 1.
What is a unit?
By default the &quot;units&quot; are dimensionless. But you can make them be meters or inches by selecting &quot;Metric&quot; or &quot;Imperial&quot; from the &quot;Length&quot; menu under the Scene panel


Blender 2.8 Alpha
In Blender 2.8 Alpha the base grid is infinite. The units are Meters by default.