Customize menu > Grid And Snap Settings > Home Grid tab
Main toolbar > Right-click 3D snap toggle.
The Home Grid panel of the Grid And Snap Settings dialog sets the spacing and other characteristics of the home grid. Choosing useful home grid settings can simplify the construction process. The home grid provides a visual reference to use when creating objects in a scene.
In the software, grids have these primary uses:
To set major grid divisions for multiple units:
From the menu bar, choose Customize menu > Grid And Snap Settings.
Click the Home Grid tab.
Adjust the Major Lines Every Nth Grid Line value, which is the number of grid squares between major lines. The minimum is 2.
For example, if you use a grid spacing of one centimeter, you might use a value of 10 so the major grid divisions represent one decimeter.
In perspective viewports, you can set a fixed size for the displayed home grid. If Inhibit Perspective View Grid Resize is turned off however, the grid size adjusts as you zoom in or out.
To allow subdivision below grid spacing:
From the menu bar, choose Customize menu > Grid And Snap Settings.
Click the Home Grid tab.
Turn off Inhibit Grid Subdivision Below Grid Spacing.
When you turn off this box, you can zoom indefinitely "deep" into any plane of the home grid. Each grid square subdivides into the same number of smaller grid spaces.

Grid spacing—Grid spacing is the size of the grid's smallest square. Use this spinner to adjust the spacing (which is in current units), or enter the value directly.
For example, if you have units set to centimeters, you might make one grid space equal to 1.000 (one unit, or one centimeter in this case).
Major Lines every Nth Grid Line—The home grid displays heavier or "major" lines to mark groups of grid squares. Use spinner to adjust the value, which is the number of grid squares between major lines, or you can enter the value directly, the minimum is 2.
For example, if you use a grid spacing of one centimeter, you might use a value of 10 so the major grid divisions represent one decimeter.
Perspective View Grid Extent—Sets the size of the home grid in the Perspective viewport.
This value is specified in terms of the Grid Spacing value, and represents the length of half the grid along an axis. This means that if Grid Spacing=10.0 and Perspective View Grid Extent=7, you will have a grid that is 140 x 140 units in size.
Inhibit Grid Subdivision Below Grid Spacing—Causes 3ds max to treat the grid as a fixed set of lines when you zoom in on the home grid. In effect, the grid stops at the grid space setting. If you keep zooming, the fixed grid is lost from view. Zooming out is not affected. When you zoom out, the home grid expands indefinitely to maintain the major grid divisions. Default=on.
When this is turned off, you can zoom indefinitely into any plane of the home grid. Each grid square subdivides into the same number of smaller grid spaces.
For a grid spacing of one centimeter and a major division of 10, the next level down subdivides into millimeter spaces, and so on.
Inhibit Perspective View Grid Resize— Causes 3ds max to treat the grid in the Perspective viewport as a fixed set of lines when you zoom in or out. In effect, the grid maintains one size, no matter how much you zoom. Default=on.
When this is turned off, the grid in the Perspective viewport will subdivide to adjust its size when you zoom in or out.
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