MGRS and UTM are often used interchangeably, and that makes sense: they are closely related. Yet they are not the same. In short, UTM is the underlying projection and MGRS is a more compact grid notation on top of it.
UTM in brief
Universal Transverse Mercator divides the earth into 60 zones of 6° and gives a position within each zone as an easting and northing in meters, plus the hemisphere (north/south). A UTM coordinate looks like this, for example: 31U 712345 5805890.
MGRS in brief
MGRS uses exactly the same projection but replaces the large numbers with letters: the grid zone and a two-letter 100 km square. The same position then becomes, for example, 31U ET 12345 05890. Shorter, and without a separate hemisphere indication.
The key differences
| UTM | MGRS | |
|---|---|---|
| Notation | Zone + large numbers (meters) | Zone + letters + short numbers |
| Length | Longer | More compact |
| Hemisphere | Indicated separately | Contained in the latitude band letter |
| Passing over radio | More error-prone | Simpler |
| Typical use | GIS, surveying | Military, field navigation |
When do you choose which?
If you work in a GIS environment or with survey data, UTM is common. If you are in the field and have to communicate positions briefly and without errors, MGRS is more convenient. Because they share the same projection, converting between the two is straightforward.
Both in MilMap
MilMap lets you choose which format you see per map and converts effortlessly between MGRS, UTM and latitude/longitude. That way you work together with people who use a different system, without converting by hand.