Guide
Map Grid References: A Complete Guide
A map grid reference is a short code that names a square on a map, so two people can point at the same place without reading out a full coordinate. You read it from the largest area to the smallest, and every extra pair of digits makes the square ten times smaller. MGRS, the grid NATO forces use on land, divides the Earth into 6° by 8° grid zones, then 100 km squares, then metric squares down to a single meter.
How to read a grid reference
Read the larger square first, then refine. For MGRS that means the grid zone and 100 km square (for example 18S UJ), then the easting digits, then the northing digits: read right, then up. More digit pairs mean finer precision, from a 100 km square down to a single meter. On a simple row-column grid, state the column letter first and then the row number ("C5", not "5C") so callouts stay consistent. For worked 6, 8 and 10-figure examples, read How to Read a Military Grid Reference.
Grid systems and their precision
Custom metric grid
A custom metric grid divides the map into equal squares of a size you choose, from 10 m up to 2,000 km, with letters along the columns and numbers down the rows. A reference like C5 names one square, so on a 100 m grid it places a point to within 100 m. Nobody needs to know zones or datums to use it, which suits event crews and search teams working one area.
MGRS (Military Grid Reference System)
An MGRS reference is a grid zone designator, a two-letter 100 km square and an even number of digits split between easting and northing, as in 18S UJ 23478 06483. The digit count sets the precision: 2 + 2 digits name a 1 km square, 3 + 3 a 100 m square, 4 + 4 a 10 m square and 5 + 5 a 1 m square. It is the grid NATO and allied forces use on land.
UTM (Universal Transverse Mercator)
UTM splits the world into 60 zones, each 6° of longitude wide, and gives a position as a zone, a latitude band or hemisphere, and an easting and northing in meters, such as 18S 323478 4306483. Eastings count from a false origin 500,000 m west of the zone's central meridian, and northings count from the equator. MGRS is the same grid with the leading digits replaced by the 100 km square letters.
Latitude and longitude
Latitude and longitude give a point as angles: 0° to 90° north or south of the equator, and 0° to 180° east or west of Greenwich. In decimal degrees each extra decimal place is ten times finer, so 4 decimals locate a point to about 11 m and 5 decimals to about 1.1 m. It is what GPS receivers and phone apps report by default.
Maidenhead locator
The Maidenhead locator used in amateur radio alternates letter and digit pairs, longitude first: a field is 20° by 10°, a square 2° by 1° and a subsquare 5′ by 2.5′. A 6-character locator such as JN58td names a rectangle about 4.6 km tall and 4 to 9 km wide, depending on latitude.
GARS (Global Area Reference System)
GARS names areas, not points. Three digits for a 30′ longitude band and two letters for a 30′ latitude band make a 5-character cell such as 380MK, about 55 km tall; a sixth character picks one of four 15′ quadrants and a seventh one of nine 5′ keypads, about 9 km across. It is used to deconflict and assign areas when air and ground units work together.
Plus Codes
Plus Codes (Open Location Code) cut the world into 20 by 20 sub-cells, two characters per step. The first 8 characters name a block about 275 m across, and the standard 10-character code, such as 8FVC9G8F+6X, a cell about 14 m by 14 m. They work as street addresses where roads have no names or buildings no numbers.
Grid zones and 100 km squares
MGRS starts from the 60 UTM zones, each 6° of longitude wide and numbered 1 to 60 eastward from 180° W. Each zone is cut into 20 latitude bands lettered C to X (I and O are skipped), 8° tall from 80° S to 84° N, with the top band X stretched to 12°. A zone number plus a band letter, such as 18S, is the grid zone designator, and about 1,200 of them cover the globe. Two areas break the pattern: zone 32V is widened over southwest Norway, and zones 31X to 37X are reshaped around Svalbard. Beyond 84° N and 80° S, MGRS switches to the polar UPS grid.
Each grid zone is then divided into squares 100 km on a side, and each square gets a two-letter ID. The first letter is the column (A to Z without I and O, cycling every three zones) and the second is the row (A to V without I and O, repeating every 2,000 km north). Because the pair repeats, UJ alone names many squares while 18S UJ names exactly one. Squares along a zone boundary are cut short where the boundary crosses them.
To see this on a real map, open the MGRS grid on the MapGridder map, zoom out to a whole country to see the grid zones, then zoom in through the lettered 100 km squares down to 10 km, 1 km and finer.
Frequently asked questions
What is a map grid reference?
A grid reference is a short code that names a square on a map. A grid divides the map into evenly spaced cells, and the reference identifies one cell (and, with more digits, a point inside it), so two people reading the same map can name the same spot without trading full coordinates.
What is the difference between MGRS, UTM, and lat/long?
Lat/long gives an angle on the globe in degrees. UTM projects the world into 60 zones and measures in meters east and north. MGRS is built on UTM but writes the position as a compact alphanumeric grid reference (for example 30U XC 9931 1016), which is faster to call out than a long decimal coordinate.
How precise is an MGRS grid reference?
The digits set it: 2 + 2 digits name a 1 km square, 3 + 3 a 100 m square, 4 + 4 a 10 m square and 5 + 5 a 1 m square. The zone and letters alone name a 100 km square.
How do I put a grid on a map?
Open the MapGridder map, pick a custom metric grid or the MGRS grid, set the spacing, color and labels, then export the map as an image or a print-ready PDF.
Are these grid tools free?
Yes. The grid overlay and converters run in your browser with no login or install; a quick, free sign-in is only needed to export a finished map. Personal and non-commercial use is free; commercial use needs a paid license.
Working with GPS tracks and map files instead? See the GPX and KML guide.