What is a Maidenhead locator?

The Maidenhead Locator System encodes a position on Earth as a short alphanumeric grid square, widely used by amateur radio operators. A code like IO91WM identifies a small rectangle, and longer codes pinpoint a smaller area.

How precise is a 4, 6 or 8 character grid?

A 2 character field spans 20 deg longitude by 10 deg latitude. A 4 character square is 2 deg by 1 deg, a 6 character subsquare is about 5 by 2.5 arc-minutes, and an 8 character grid narrows that another tenfold.

Why does the tool return the center of the square?

A locator describes an area, not a single point. Returning the geometric center of the cell gives the most representative single coordinate for that grid.

Is case sensitivity a problem?

No. The field and subsquare letters are conventionally upper and lower case respectively, but this converter uppercases the input so IO91wm and IO91WM give the same answer.

Which character lengths are supported?

Two, four, six and eight character locators are accepted. Odd lengths are rejected because the format always alternates a latitude and longitude character in pairs.

Maidenhead Locator to Lat/Lng

Maidenhead grid squares

The Maidenhead Locator System, also called the QTH locator, packs a global position into a short code such as IO91WM. Amateur radio operators use it to exchange locations compactly and to compute distances between stations. Each pair of characters refines the position: the first pair selects a large field, the second a square within it, the third a subsquare, and the fourth an extended square.

How it works

The grid divides the world from the south pole and the antimeridian. The first character pair (letters A to R) splits longitude into 18 bands of 20 degrees and latitude into 18 bands of 10 degrees. The second pair (digits 0 to 9) divides each band into ten, giving 2 degrees of longitude and 1 degree of latitude. The third pair (letters A to X) divides by 24, and the fourth pair (digits 0 to 9) divides by another ten.

IO91WM  ->  field IO + square 91 + subsquare WM

Adding the running offsets and returning the center of the final cell yields the latitude and longitude.

Example and tips

The locator IO91WM resolves to roughly 51.46 N, 0.21 W near London. Longer locators are more precise, so prefer a 6 or 8 character grid when accuracy matters. Because a locator names an area, two nearby points can share the same short code, which is expected behaviour rather than an error.