How the Maidenhead locator works
The Maidenhead Locator System gives radio amateurs a short code for where they are. Instead of reading out two long coordinates, you send six characters like IO83vl. It was adopted by VHF managers at a meeting in Maidenhead, England, in 1980, and it is now used worldwide for contests, awards, satellite work and digital modes like FT8, which sends your four-character square with every CQ.
Each pair of characters zooms in on the one before it:
| Pair | Name | Characters | Size (longitude × latitude) | Roughly |
|---|---|---|---|---|
| IO | Field | A to R | 20° × 10° | 2,000 × 1,100 km |
| 83 | Square | 0 to 9 | 2° × 1° | 130 × 110 km in the UK |
| vl | Subsquare | a to x | 5′ × 2.5′ | 5.5 × 4.6 km in the UK |
| (digits) | Extended square | 0 to 9 | 30″ × 15″ | about 550 × 460 m |
Longitude always comes first in each pair, then latitude. The grid starts at 180° west and 90° south, which is why every letter and number counts upward as you move east and north.
Working it out by hand
For Manchester, at latitude 53.4808 and longitude −2.2426:
- Add 180 to the longitude and 90 to the latitude so nothing is negative: 177.7574 and 143.4808.
- Field: divide the longitude by 20 (8.89, so the 9th letter, I) and the latitude by 10 (14.35, so the 15th letter, O). Field IO.
- Square: take what's left over (17.7574 and 3.4808), divide the longitude part by 2 (8.88, so 8) and keep the whole degrees of latitude (3). Square 83.
- Subsquare: take the remainders again (1.7574 and 0.4808), multiply the longitude part by 12 (21.1, so the 22nd letter, v) and the latitude part by 24 (11.5, so the 12th letter, l). Subsquare vl.
The calculator above does exactly this, then goes one level further for the 8-character extended square.
Distance and beam headings
The distance tool uses the centre of each square and calculates the great-circle path, which is the shortest route over the Earth's surface. With six-character locators the answer is usually within a few kilometres. The heading is the direction to point a beam from the first station, measured clockwise from true north. If you set up with a compass, remember that magnetic north in the UK is currently within a couple of degrees of true north, but in much of North America the difference is 10° or more.
The long path is the other way round the globe. On HF it sometimes opens when the short path doesn't, particularly around sunrise and sunset, so it's worth knowing both headings.
Questions
What is my grid square?
Press “Use my location” above and the calculator reads your device's GPS and shows your 4, 6 and 8-character locator. Nothing is sent to a server. You can also type in coordinates from a map.
What's the difference between a QTH locator and a grid square?
They're the same thing. QTH locator is the common name in Europe, grid square is more common in North America, and both mean the Maidenhead Locator System.
Should I give 4 or 6 characters?
FT8 and most VHF contest exchanges use 4 characters. Six characters are normal for VHF, UHF and microwave contacts where the exact distance scores points, and for satellite and SOTA logging.
Is the grid square the same as my postcode or ZIP code?
No. A UK subsquare covers about 25 square kilometres, so it's far larger than a postcode, and grid lines don't follow any administrative boundaries.