This tool converts decimal latitude and longitude to a Maidenhead Locator (also called a QTH locator or grid square), the compact grid-reference system used throughout amateur radio for contests, beacons and grid hunting. It outputs a 4, 6 or 8 character code such as IO91wm.
How it works
Both coordinates are first made positive by shifting:
adjLng = longitude + 180 (0 to 360)
adjLat = latitude + 90 (0 to 180)The result is then encoded in pairs, each level dividing the previous cell:
- Field — two letters A to R:
adjLng / 20,adjLat / 10 - Square — two digits 0 to 9: each field split into 10 along longitude and latitude
- Subsquare — two letters a to x: each square split into 24 along longitude and latitude
So a 6-character locator like IO91wm pins a point to within a few kilometres. By convention the field letters are upper case and the subsquare letters lower case.
When and why hams use locators
Contests — most VHF/UHF/microwave contests award points based on the number of unique grid squares worked. Operators confirm the exchange (signal report + locator) for each contact. Working a rare or distant grid square scores higher than a local one. Having your own locator exactly right matters because contest loggers verify it against your coordinates.
Beacon registration — propagation beacons broadcast their locator in CW or data modes so listeners can calculate bearing, distance, and path type. IARU coordinated beacons all carry registered locators.
Grid hunting (SOTA, POTA, WWFF) — Summits on the Air and similar awards often track grid activation. Operators chasing a reference confirm the activator’s locator as part of logging.
DX clustering and reverse beacons — spotting networks add the locator automatically when a callsign’s home location is known, helping other stations evaluate propagation direction.
Precision levels in practice
| Characters | Cell size (approx.) | Typical use |
|---|---|---|
| 4 (field + square) | ~100 km × 100 km | Quick DX identification, country-level planning |
| 6 (+ subsquare) | ~5 km × 5 km | Standard contest exchange, beacon registration |
| 8 (+ extended subsquare) | ~300 m × 300 m | Antenna aiming, precise APRS position |
Most operators and contests use the 6-character locator as the standard. An 8-character locator is useful for close-range VHF work where fine bearing calculation matters, or for accurate position in APRS/packet stations.
Notes on reading your result
The locator encodes the south-west corner of the cell that contains your point — it is a grid reference, not a geocoded pin. Two stations both claiming IO91wm could be up to about 5 km apart. Everything runs in your browser. Pair it with the DMS converters when working from chart coordinates, or use the companion tool to convert a locator back to a lat/lng centre point.