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QTH locator calculator

Why half the calculators out there lie

A locator names not a point but a cell — at six characters, roughly 9 × 6 kilometres at our latitudes. The reverse conversion should return its centre, and that is where most implementations go wrong: they give the south-west corner and shift the position by several kilometres, systematically.

centre of the squarethe coordinates are for the centre,not for the corner of the square
A locator names a square, not a point: the coordinates returned are those of its centre
Conversion direction
Latitude (°, south is negative)
Longitude (°, west is negative)
Accuracy
Result
Locator
Cell centre
Cell size
Cell bounds in latitude
Cell bounds in longitude

📐 The algorithm​

Coordinates → locator:

x = (longitude + 180) / 20        y = (latitude + 90) / 10
field:     'A' + floor(x),          'A' + floor(y)
square:    '0' + floor(frac(x)·10),  '0' + floor(frac(y)·10)
subsquare: 'a' + floor(frac(x·10)·24), 'a' + floor(frac(y·10)·24)

Then another pair of digits (8 characters) and another pair of letters (10 characters).

Locator → coordinates:

longitude = −180 + 20·field + 2·square + (2/24)·subsquare + half a step
latitude  =  −90 + 10·field + 1·square + (1/24)·subsquare + half a step

Cell size:​

CharactersStep in latitudeStep in longitude
41°2°
62.5′5′
815″30″
100.625″1.25″
Where this calculator stops:
  • It returns the centre of the cell, not its corner — otherwise a systematic offset appears
  • A locator describes an area, so a distance between two locators is only accurate to the size of a cell
  • The field is limited to the letters A–R: the system covers the whole globe, but fields S–Z are unused
  • At the poles and on the 180th meridian the cells degenerate — that is normal, but neighbours there are worked out with care

🎯 In practice​

  • Filling in the log — a locator is needed in every VHF contact.
  • Preparing for a contest: the eight neighbouring squares are shown in the table straight away.
  • Checking someone else's locator: is it really where they say it is.
Practical advice:
  1. Six characters is standard for ordinary contacts; eight only makes sense on microwaves.
  2. The canonical case is KO50gk, but any case is accepted on input.
  3. Put coordinates from a phone in as they are: GPS is accurate enough even for 10 characters.
  4. A locator near a cell boundary is a reason to check the coordinates again: a neighbour 200 metres away already has a different one.

© 2026 UR3PKI · CyberDev.Space · Content licensed under CC BY-NC-SA 4.0.

How to cite this calculator
UR3PKI. «QTH locator calculator». CyberDev.Space. https://cyberdev.space/en/radio/calculators/others/maidenhead (licence CC BY-NC-SA 4.0).

The licence lets you use this material freely, including in teaching materials, but only with attribution to the author and a link to the source.

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