Location technology
MGRS: The Military Grid Reference System
MGRS is a grid notation built on UTM that names squares with letters and digits. Learn how to read one and how precision is set by digits.
Updated 14 October 2026 · 3 min read
The Military Grid Reference System, MGRS, is a standard way of writing a location as a short alphanumeric string. It is built on the UTM grid, and is used by NATO armed forces and by some civil and emergency organisations. A reference names a square of a chosen size, rather than an infinitely small point.
Structure of a reference
An MGRS reference has parts that read from large to small:
- Grid zone designator: the UTM zone number and a latitude band letter, for example 18S.
- 100 km square identifier: two letters that name one 100 km by 100 km square within that zone.
- Numerical location: an even number of digits, split into an easting half and a northing half, giving the position inside the square.
A full example looks like 18S UJ 23480 06470, usually written without spaces. The letters narrow the area, and the digits locate a spot within it.
How digits set the precision
The more digits, the smaller the square being identified:
| Digits (total) | Square size |
|---|---|
| 2 | 10 km |
| 4 | 1 km |
| 6 | 100 m |
| 8 | 10 m |
| 10 | 1 m |
You can shorten a reference by deleting digits from the end of each half, which makes the area larger rather than moving the point. This gradual loss of precision is a deliberate feature of the system and is useful when only an approximate location is needed.
Why it is useful
- Compact and unambiguous: no signs, hemispheres or decimal points.
- Easy to communicate by voice or radio: letters and digits can be read out clearly.
- Scalable: a user can give a coarse or fine reference depending on need.
Limitations
- It depends on the UTM zone structure, so references near zone boundaries need care.
- The letters and digits are not self-explanatory to a general audience.
- It is not designed for everyday address use and is not widely supported in consumer apps.
Where it fits among location systems
MGRS belongs to the family of grid-based notations, alongside geohash, Plus Codes and others. Each divides the world into cells and names them, but with different structures, alphabets and intended audiences. A system such as UPCS serves a different purpose: a short, memorable code for a 3 m by 3 m cell, intended to accompany a normal postal address in daily use rather than for military mapping.
Frequently asked questions
Is MGRS the same as UTM?
MGRS is a different way of writing positions that is based on the UTM grid. It uses grid zone letters and 100 km square letters followed by digits.
Does MGRS identify a point or an area?
An area. The number of digits sets the size of the square, so fewer digits means a larger square.