Short answer
A compact alphanumeric grid coordinate system built on top of UTM, used by NATO, US DoD, aviation, and search-and-rescue. A typical MGRS reference like 33TUM1234567890 encodes a position to 1 m precision in 15 characters — survives voice transmission and SMS reliably.
Detailed explanation
MGRS extends UTM with two layers of letter coding. The first layer is a latitude band letter (C–X, omitting I and O, covering 8° latitude bands from 80°S to 84°N). The second is a pair of letters identifying the specific 100 km × 100 km grid square within the UTM zone. The remaining easting and northing digits identify the position within the 100 km square, with precision controlled by digit count: 10 digits (5+5) = 1 m, 8 digits = 10 m, 6 = 100 m, 4 = 1 km, 2 = 10 km.
A complete MGRS reference like 33T UM 12345 67890 reads as: UTM zone 33, latitude band T (40°N–48°N), 100 km square UM, easting 12345 m + northing 67890 m within that square. The compact form 33TUM1234567890 (no spaces) is what you'd transmit by voice or text — "three-three-tango-uniform-mike" leaves no room for ambiguity.
MGRS is the standard position format for NATO ground operations, US military (Army, Air Force, Navy), aviation search-and-rescue (CAP / RCC), and many civilian SAR organisations. The redundancy in the letter codes makes it robust to voice-radio errors in a way that decimal lat/lon is not.
Conversion to and from MGRS is layered on top of UTM — the Coordinate Converter on this site handles the bidirectional mapping using the standard NGA TM 8358.1 grid letters.
Try it interactively
Coordinate Converter
Open the toolRelated terms
UTM
A worldwide projection system that divides Earth into 60 6°-wide longitude zones, each projected as a transverse Mercator centred on its meridian. Distances and areas inside one zone are easy linear-metric computations; the projection is valid 80°S to 84°N latitude.
WGS84
The reference ellipsoid and datum used by GPS and the de-facto GNSS standard. Semi-major axis a = 6378137 m, flattening f = 1/298.257223563. Position differences from local datums (NAD83, ETRS89, GDA2020, CGCS2000) range from tens of cm to several metres depending on region.