USNG to latitude and longitude
Decodes a U.S. National Grid reference, including a truncated local one like NE 863 777 when you give the grid zone, to the center and south-west corner of the square it names.
The 100 m square is centered at 40.445922835°, -79.981752606°.
- Center longitude
- South-west corner latitude
- South-west corner longitude
- Square size
Provenance
- Computed by
- geodesy.grid-ref.usng-inverse 1.0.0, core 0.1.0
- Model
- USNG = MGRS on NAD 83/WGS 84; the square's center and corner by inverse UTM or UPS
- Accuracy
- Identical to GeographicLib's MGRS decoding (GeoConvert) within 1e-9°
- Notes
- None
- Cites
- Federal Geographic Data Committee, United States National Grid, FGDC-STD-011-2001
Something look off?
How we got thisFormula, worked example, sources, and proof
Model: USNG = MGRS on NAD 83/WGS 84; the square's center and corner by inverse UTM or UPS
Accuracy: Identical to GeographicLib's MGRS decoding (GeoConvert) within 1e-9°
When to use this: Use this to read a US National Grid reference, including the truncated local form used on a single map sheet, such as NE 863 777, when you supply the grid zone. It returns the center and south-west corner of the square. It is what a dispatcher or a team member does with a grid reference passed by radio: read it back as coordinates and plot it.
Limitations: A truncated local reference repeats every 100 km, so without the grid zone and square it can name more than one place; this is why the zone is asked for. The square's size is the precision, and the center is for plotting rather than a position report. USNG and MGRS share their geometry but not always their spacing conventions, so a reference copied between systems should be checked rather than assumed identical.
Worked example: A truncated reference near Pittsburgh. Source: add-geodesy-suite requirement: truncated USNG in a known grid zone. It is golden test vector v020, and every build checks the tool still gives its answer within its tolerance.
You enter
- USNG reference
- NE 863 777
- Grid zone
- 17T
You get
- Center latitude
- 40.445922835°
- Center longitude
- -79.981752606°
- South-west corner latitude
- 40.445477643°
- South-west corner longitude
- -79.982348916°
- Square size
- 100 m
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: 22 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
- 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
Learn the concept: MGRS and USNG coordinates explained