Latitude and longitude to USNG

Model: USNG = MGRS on NAD 83/WGS 84, written with spaces; truncated, never rounded

Accuracy: Identical to GeographicLib's MGRS (GeoConvert) on the test points

When to use this: Use this for the US National Grid form, written with spaces, which US civilian agencies and emergency management use on maps and in reports. Give a position and it returns the reference truncated to the precision you choose. It is the form printed on US topographic maps and used by emergency management, so a position given this way can be read straight off a paper map by someone with no equipment.

Limitations: USNG shares MGRS geometry, so the reference names a square and truncates rather than rounds, and its precision is the size of that square. It is defined on WGS 84 or NAD 83, which differ by about a meter; a reference is only as good as the datum behind the coordinates you gave. Spacing and precision are part of the convention: a reference written without its spaces, or truncated further than intended, names a larger square than the writer meant.

Worked example: Pittsburgh at 1 m. Source: add-geodesy-suite scenario: 17T NE 86309 77770. It is golden test vector v001, and every build checks the tool still gives its answer within its tolerance.

Review: Not yet independently reviewed by a geodesist.

Last verified: 2026-09-19, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.0.0, core 0.1.0. See this tool in the verification report.

Changes

• 2026-09-19, changed: The GARS, GEOREF, Maidenhead, and USNG tools are stable, both directions. They reproduce NGA's GARS band definitions, the Wikipedia GEOREF (NAS Patuxent River) and Maidenhead (W1AW) examples, and the FGDC USNG Washington Monument, and match GeographicLib, pygeodesy, an exact Maidenhead reference, and NGA GEOTRANS on thousands of points. Results are unchanged apart from the fix below. Changelog

Checked against: 23 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

• United States National Grid, FGDC-STD-011-2001, Federal Geographic Data Committee, FGDC-STD-011-2001. Sections 2 and 3: grid zone, 100,000-meter square, and truncated references.

Terms

MGRS: Military Grid Reference System

UTM and UPS coordinates written as a zone, a latitude band, a two-letter 100 km square, and digits, like 17T NE 86309 77770. Source: NGA.STND.0037 MGRS

USNG: United States National Grid

MGRS as adopted for US civilian use on NAD 83, usually written with spaces between its parts. Source: United States National Grid