How to read an MGRS grid reference

The parts of a grid

Here's a full grid for a spot near Lake Eola in Orlando, Florida: 17R MM 63501 57423.

Part	Name	What it tells you
17	Zone	One of 60 north–south strips around the world, each 6° of longitude wide.
R	Latitude band	A letter for a slice of latitude, usually 8° tall. Zone and band together are the grid zone designator.
MM	100 km square	Two letters naming one 100 km by 100 km square in that zone.
63501	Easting	How far east you are across the square.
57423	Northing	How far north you are up the square.

Read right, then up

The digits always split evenly. The first half is the easting and the second half is the northing. Read them in that order: go right across the map, then up. Six digits such as 635 574 mean 635 right and 574 up.

What the number of digits means

More digits name a smaller square, not a more accurate position.

Digits	Example	Square size
2	17R MM 6 5	10 km
4	17R MM 63 57	1 km
6	17R MM 635 574	100 m
8	17R MM 6350 5742	10 m
10	17R MM 63501 57423	1 m

Shorten by cutting, never by rounding

To shorten a grid, drop digits from the end of each half. 63501 57423 becomes 635 574, not 636 574. The result still names the square your point is in, and that square's numbers are measured from its lower-left corner.

Check these before you trust a grid

The whole reference. Digits alone repeat every 100 km, so a grid without its square letters only works when everyone knows the area.
The datum. Older maps may use NAD27, and the same place then has different numbers. The map's margin says which datum it uses.
The ground. Check your position against terrain, and carry a map and compass.

Try it

Paste any grid into the free MGRS converter to see it as UTM and latitude and longitude, or read how USNG differs. Gridmark shows and enters these grids offline on iPhone, iPad and Apple Watch.