What is a Maidenhead Grid Square and How Do I Find Mine?

If you've tried to use a satellite pass predictor, entered a contest, or talked to a VHF operator, you've probably encountered grid squares. "What's your grid?" is one of the most common questions in ham radio. Here's what Maidenhead grid squares are, why the ham radio community uses them, and how to find yours.

What is a Maidenhead Grid Square?

A Maidenhead grid square (also called a Maidenhead locator or QTH locator) is a compact way of describing your location on Earth using a short alphanumeric code. The system was developed at a meeting in Maidenhead, England in 1980 and has been the standard location reference in amateur radio ever since.

The world is divided into a grid of fields, squares, and subsquares. A typical grid square reference looks like FN25 or IO91 — two letters followed by two numbers. Extended six-character references like FN25dg add a final pair of letters for higher precision.

The system works hierarchically:

• Field — two letters (e.g. FN) — covers a 20° longitude × 10° latitude area
• Square — two numbers (e.g. FN25) — divides the field into 100 squares, each 2° × 1°
• Subsquare — two more letters (e.g. FN25dg) — divides the square into 576 subsquares, about 5km × 2.5km

For most purposes a four-character grid square (like FN25) is sufficient. For satellite work and precise VHF contests, six characters are preferred.

How to Find Your Grid Square

There are several easy ways:

Option 1 — Use Ham Sat Tracker
Open Ham Sat Tracker and tap the 📍 locate button. It reads your GPS coordinates and converts them to a grid square automatically, filling in the location field for you.

Option 2 — Online lookup
Go to qrz.com/gridmapper or search "Maidenhead grid square lookup" — enter your address or click your location on the map and it shows your grid square instantly.

Option 3 — Calculate it manually
If you know your decimal latitude and longitude (e.g. 45.4215°N, 75.6972°W for Ottawa) you can calculate the grid square:

1. Add 180 to your longitude: 75.6972W = -75.6972, so -75.6972 + 180 = 104.3028
2. Divide by 20, take the integer: 104.3028 / 20 = 5 → letter F (A=0, B=1... F=5)
3. Remainder × 10, take integer for second letter field: (104.3028 mod 20) / 2 = 2 → N
4. Repeat similar steps for latitude to get the numbers

In practice just use a lookup tool — the manual calculation is error-prone.

Why Ham Radio Uses Grid Squares

Giving a precise street address over the air is impractical and raises privacy concerns. Decimal coordinates like 45.4215, -75.6972 are accurate but unwieldy to read phonetically. A grid square like FN25 is short, easy to say on the air, and gives enough location information for most purposes.

Grid squares are used in:

• Satellite pass prediction — Ham Sat Tracker uses your grid square to calculate exactly when satellites will be above your horizon
• VHF/UHF contests — grid squares are the standard exchange in most VHF contests. Contacting stations in different grids scores points.
• Awards — the Worked All States equivalent for VHF is often based on grid squares rather than state boundaries
• SOTA and POTA activations — portable operators frequently report their grid square
• APRS — position beacons often include grid square information
• DX contacts — giving your grid helps the other station confirm location and propagation path

Grid Squares Around the World

Some examples to give you a sense of the scale:

• FN25 — Ottawa, Canada
• EM72 — Nashville, Tennessee
• DM33 — Phoenix, Arizona
• IO91 — London, England
• PM74 — Tokyo, Japan
• QF22 — Sydney, Australia

The first letter of the field tells you roughly which part of the world you're in. Fields starting with F, G, H cover most of North America. I, J, K cover Europe. P, Q cover Asia and the Pacific.

Six-Character Grid Squares for Satellite Work

For satellite pass prediction, a four-character grid square is accurate to within about 100km — enough for pass times to be within a minute or two of actual. A six-character subsquare narrows this to about 5km, which improves pass time accuracy to within seconds.

Ham Sat Tracker accepts both four and six character grid squares. If you're doing serious portable satellite work from a specific location, using a six-character grid gives you the most accurate predictions. For general use from a home location, four characters is fine.

Your Grid Square on QRZ

Make sure your grid square is correctly listed on your QRZ.com profile — it's used by logging software, contest adjudication, and other hams verifying contacts. Log into QRZ, go to your callsign page, and check the grid square field in your bio. If it's blank or wrong, update it.

73 de VE3AKK