Maidenhead Grid Square Calculator - Locator from Latitude and Longitude

Amateur radio operators use Maidenhead locators to describe a location in just a few characters. Enter your latitude and longitude and this tool gives your locator, or enter a locator and it decodes it back to coordinates. It is free, instant, and needs no account.

What a Maidenhead locator is

A Maidenhead locator, also called a grid square, is a short code for a place on Earth, designed for amateur radio. A six-character locator such as IO91wm describes a rectangle about 5 minutes of longitude wide and 2.5 minutes of latitude tall, small enough to aim an antenna or to log a contact, but short enough to speak over the radio. The first two letters name a large field, 20 degrees of longitude by 10 degrees of latitude. The next two digits narrow it to a square of 2 degrees by 1 degree. The last two letters narrow it again to the subsquare. An eight-character extended locator adds two more digits for even finer precision. The system covers the whole planet with the same rules, which is why it works for contacts between any two stations.

How the encoding works

Encoding starts by shifting longitude and latitude so that both are positive: add 180 to longitude and 90 to latitude. The field letters come from dividing the shifted longitude by 20 and the shifted latitude by 10, then converting the results to letters, with A as zero. The square digits come from the remainders: divide the leftover longitude by 2 and the leftover latitude by 1, and keep the whole numbers. The subsquare letters come from the next remainders, divided into 24 parts each. Decoding runs the same steps backwards and returns the south-west corner of the square, because a locator names a rectangle, not a single point. This tool follows those steps exactly, so its output matches other Maidenhead calculators.

How to use the calculator

To encode, enter your latitude and longitude in decimal degrees, using a minus sign for south latitudes and west longitudes. London, for example, is about 51.5 latitude and -0.12 longitude, which encodes to IO91wm. Press the button and the tool shows the six-character locator and the eight-character extended version, plus a breakdown of field, square and subsquare. To decode, type a locator such as FN20xr, which is part of New York, and press decode. The tool returns the south-west corner of that square, which you can drop into any map.

Why radio operators use locators

Locators are faster and less error-prone than full coordinates on voice radio, where every digit is a chance to mishear. They are the standard for VHF and UHF awards, contests and distance records, where the locator of each station proves the contact and its distance. They also protect privacy: a six-character locator places you within a few kilometres, which is enough for radio purposes without giving your home address. Many logging programs, contest tools and propagation maps accept locators directly, so knowing yours saves time every time you operate. Even shortwave listeners use locators to note where a signal was heard.

Common mistakes to avoid

The most common mistake is swapping latitude and longitude, which lands you in the wrong field entirely. Always enter latitude first in this tool, as labelled. Another mistake is using the wrong sign: west longitudes and south latitudes are negative, and forgetting the minus sign mirrors your location across the globe. A third mistake is treating the decoded point as exact: it is the south-west corner of the square, so the true station may be up to a few kilometres north or east of it. For antenna aiming, use the centre of the square, which you can estimate by adding half the square’s size to the decoded corner.

Limits

The calculator does pure coordinate math. It does not check whether your coordinates are on land, and it does not fetch your location: you enter the numbers yourself, so a typo gives a valid-looking but wrong locator. Double-check your coordinates against a map before logging them. The tool also does not convert between locator systems, such as the older QRA system. Everything runs in your browser, with no account and no data sent anywhere.

Maidenhead Grid Square Calculator – Locator from Latitude and Longitude