Download U.S. National Grid Tools for ArcGIS

To start using U.S. National Grid Tools for ArcGIS, you need to go through the following steps:

Uninstall any previous versions of U.S. National Grid Tools for ArcGIS before installing a newer version.
Ensure that you have administrator privileges on the machine and that you have write permissions to C:\Program Files directory.
Select the version for download:
U.S. National Grid Tools for ArcGIS for 9.2
U.S. National Grid Tools for ArcGIS for 9.1
Extract the contents of the downloaded ZIP file to a directory on your local machine.
Run USNG.exe to install the U.S. National Grid Tools for ArcGIS add-on.
Start ArcMap. You must turn on the USNG Tools add-on by selecting Tools>Extensions, checking the U.S. National Grid Tools box, and clicking close.
Toggle on the U.S. National Grid Tools toolbar (select either View>Toolbars or right-click in the toolbars region near the top of ArcMap).
From here, the coordinate and grids tools are available.

At this release of the U.S. National Grid Tools for ArcGIS, USNG coordinates are supported only for the NAD 83 and WGS84 datums. When identifying USNG coordinates in the Coordinate Tool, the MGRS entry with the WGS84 datum selected should be used.
The U.S. National Grid system is based on and interoperable with the Military Grid Reference System. The main difference is the 100,000-meter grid two-letter identification. The USNG lettering scheme is identical to the MGRS 100,000-meter grid lettering scheme for NAD 83. USNG, however, uses the same 100,000-meter lettering scheme for both NAD 83 and NAD 27, whereas MGRS has two lettering schemes for quick identification between the datums. USNG coordinates indicate that the coordinates are in the NAD 27 datum by appending "(NAD 27)" to the end of the coordinate, for example