What MGRS is, and how to read a grid reference

The Military Grid Reference System (MGRS) names any spot on Earth with one short code, such as 10T ET 48894 74326, the Space Needle in Seattle. It is the grid armed forces and search-and-rescue teams use, and it is the UTM grid written with letters.

See the MGRS grid on the globe Convert coordinates

The three parts of a reference

Read 10T ET 48894 74326 from left to right:

Part	Example	What it names
Grid zone designator	10T	One of 60 zones, each 6° of longitude wide (zone 10 is 126°W to 120°W), and a band of latitude 8° tall, lettered C to X from 80°S northward (T is 40°N to 48°N). Together they name a cell about 500 km by 900 km.
100 km square	ET	Two letters for one 100 km by 100 km square inside the zone: the first letter counts squares eastward, the second northward. The letters repeat far enough apart that no two squares near each other share them.
Easting and northing	48894 74326	Meters east, then meters north, of the square's south-west corner. Always the same number of digits each: 48,894 m east and 74,326 m north here.

The letters I and O are never used, so nothing is mistaken for a 1 or a 0.

How precise a reference is

Drop digits from the end of both numbers, equally, and the reference names a larger square instead of a point. The rule people learn is "read right, then up": the easting digits come first.

Digits	Names a square of	Example
none	100 km	10T ET
2 (1 + 1)	10 km	10T ET 4 7
4 (2 + 2)	1 km	10T ET 48 74
6 (3 + 3)	100 m	10T ET 488 743
8 (4 + 4)	10 m	10T ET 4889 7432
10 (5 + 5)	1 m	10T ET 48894 74326

A reference names the square whose south-west corner it gives, so the digits are cut, never rounded. The globe's readout follows the same rule: from space it shows the 100 km square alone, and the digits grow as you fly down.

Reading the grid on a map

On a 1:50,000 map, the grid lines are 1 km apart and each carries its two "principal digits", such as 48 on an easting line and 74 on a northing line. To read a point: find the easting line to its left (48), estimate the tenths across to it (8), then the northing line below it (74) and the tenths up (3), and you have ET 488 743, a 100 m square. On the globe the lines are labeled the same way at every level: one digit on the 10 km lines, two on the 1 km lines, three on the 100 m lines.

The same grid, three ways of writing it

UTM gives the full meters in the zone: 10T 548894 E 5274326 N. The first digit of each number is what the 100 km square's letters replace. What UTM is.
USNG, the United States National Grid, is MGRS with the same letters and digits on the NAD83 datum, which differs from WGS84 by a meter or two in the lower 48 states. For most purposes they are the same reference.
Latitude and longitude: 47.6205, -122.3493, or 47°37′13.8″N 122°20′57.5″W. The globe shows all of them for the point under the cursor, and Convert coordinates turns any one into the others.

The exceptions worth knowing

Southern Norway. Zone 32 is widened to start at 3°E between 56°N and 64°N, so the whole of southern Norway falls in one zone; zone 31 is only 3° wide there. Trondheim is 32V NR 69618 34313.
Svalbard. Between 72°N and 84°N there are only four zones over the islands, 31, 33, 35 and 37, the first and last 9° wide, the middle two 12°; 32, 34 and 36 don't exist there. Longyearbyen is 33X WG 14278 83355.
Band X is taller. It runs from 72°N to 84°N, 12° instead of 8°.
The poles. North of 84°N and south of 80°S the grid is UPS, the Universal Polar Stereographic grid. Its references start with a polar zone letter instead of a zone number and band: A or B in the south, Y or Z in the north, west or east of Greenwich, as in Z GC 25425 30820. Grid Globe reads and draws them, to the poles themselves.

Try it on the globe

The Space Needle, 10T ET 48894 74326
The Eiffel Tower, 31U DQ 48251 11935
The Sydney Opera House, 56H LH 34900 52288, south of the equator, where the band letters run from C
Southern Norway from above, with the widened zone 32

Type any reference into the globe's search box and it flies there; cut digits off the end to see the larger square it names.

Used Google Earth Pro's MGRS grid? MGRS and UTM grids without Google Earth Pro shows where its settings are here.