Maidenhead locator – grid square finder and map

The Maidenhead Locator System is the grid that radio amateurs use to say where they are in a few letters and digits. It was agreed at a meeting of VHF managers in Maidenhead, England, in 1980 and is now exchanged in VHF and UHF contests, satellite and meteor scatter contacts, and in digital modes such as FT8 and WSPR, which send a four-character square with every report. This tool works in both directions. Click your station on the map, search the nearest town or press "Use my location", and it shows the locator with 4, 6, 8 and 10 characters, each with a copy button, and draws the six-character square. Or type a locator, from a two-letter field to a ten-character extended square, and the map jumps to it. The grid on the map follows the zoom, from the large fields down to subsquares and extended squares, so you can see where the boundaries run between nearby stations. Type a second locator to get the distance and the beam heading to it, with the path drawn on the map.

How to use it

1. Click your position on the map, search a town, press "Use my location", or type coordinates.
2. Read and copy the locator with 4, 6, 8 or 10 characters; the six-character square is drawn on the map.
3. Or type a locator such as JN58td and press "Show" to see that square.
4. Type a second locator under "Distance to another locator" for the distance and bearing, then share or export.

How accurate is it?

How the grid is built

The world is divided into 18 × 18 fields of 20° of longitude by 10° of latitude, named AA to RR. Each field has 10 × 10 squares of 2° by 1° (JN58), each square 24 × 24 subsquares of 5′ by 2.5′ (JN58td), each subsquare 10 × 10 extended squares of 30″ by 15″, and each of those 24 × 24 extended subsquares. The letters count eastwards from 180° W and northwards from the South Pole, on WGS84 latitude and longitude.

How big a square is

A six-character subsquare is 2.5′ of latitude, about 4.6 km, from south to north everywhere, but its 5′ of longitude shrinks from about 9.3 km at the equator to 4.6 km at 60° north. The panel shows the size of the current square on the ellipsoid. An eight-character locator narrows the position to an area of about 900 by 460 m at the equator, a ten-character one to about 40 by 20 m.

Distances between locators

When you type a second locator, the distance and the initial bearing are calculated from your clicked position, or from the centre of your square, to the centre of the other square, along the geodesic on the WGS84 ellipsoid. With six-character squares at both ends the result can differ from the true station-to-station distance by a few kilometres; contest software uses the same convention.

Good to know

Letters and digits in the right places

Locators alternate letter pairs and digit pairs: two letters A–R, two digits, two letters a–x, two digits, two letters a–x. JN58TD and jn58td mean the same square, but a mistyped letter such as "JN58ty" is not a valid locator, because subsquare letters stop at x.

Your location from the browser

"Use my location" asks the browser, which may use GPS, Wi-Fi or the network. On a laptop indoors it can be hundreds of metres off, which is fine for a six-character square but not for eight or ten characters; check the dot on the map.

Bearings are true, not magnetic

The beam heading is measured from true north, as antenna rotators are usually set up. If you align an antenna with a compass, correct for the local magnetic declination.