Use the free tool above, then read on for how it works, a worked example, and practical tips.
What this tool does
Radio amateurs swap Maidenhead grid squares instead of full addresses, but a pair of squares alone does not tell you how far apart the stations are or which way to point a beam. This calculator turns two grid squares into a distance in kilometres and miles and an initial bearing in degrees, so you can aim and log with confidence.
How it works
The tool first decodes each grid square to the centre of its rectangle, using 20 degrees of longitude and 10 degrees of latitude for the field letters, then 2 by 1 degrees for the digits, then small subsquare steps for the final letters. It then applies the haversine formula for great-circle distance on a sphere and the standard bearing formula from the first point to the second.
How to use it
- Enter your values in the boxes above.
- Press the calculate or play button.
- Read the result shown below the tool.
- Try a second set of values to compare options.
Worked example
London’s IO91wm and Munich’s JN58td sit roughly 900 kilometres apart, with an initial bearing from London of about 115 degrees, roughly south-east. That bearing is the starting direction for a great-circle path, and a beam pointed there will favour the short path even though the signal curves across the map.
Practical tips
Use four-character squares for rough planning and six-character squares when you need a bearing worth steering a directional antenna by, because the extra letters shrink the uncertainty a lot. Log the bearing with the contact, since the return bearing from the other station is roughly the opposite direction and helps both stations aim at each other.
Common mistakes
A common mistake is measuring distance on a flat map with a ruler, which overstates long paths because the Earth curves. Another is entering a grid square with the letters and digits in the wrong order, which can move the point by hundreds of kilometres without any warning from a plain map tool.
Questions and answers
Is this tool free? Yes. It runs in your browser, needs no account, and gives instant results.
Do I need to install anything? No. The tool works on any modern phone or computer browser.
How accurate are the results? The maths follows the standard formulas shown above. Real-world results vary with terrain, equipment, and conditions, so use the figures for planning.
Can I use it on my phone? Yes. The tool is designed to work on a phone screen, so you can use it at the operating desk, in the field, or at a club station without a computer.
Who uses this tool
Radio amateurs, students, and club members all use tools like this one, because they turn a formula from a book into an answer for your own station in seconds. Beginners use it to check homework and first setups, while experienced operators use it to sanity-check a plan before spending money on cable, masts, or antennas. Even a quick check can prevent a costly mistake, such as ordering the wrong cable length or aiming a beam in the wrong direction.
What to try next
- Run the tool with your real station values, not just the default numbers, so the answer means something for your setup.
- Change one input at a time and watch how the result moves, because that shows you which input matters most.
- Write the result in your station notebook next to the date, so you can compare later changes against a known baseline.
Safety note: this is an educational estimator only. Real transmissions need an amateur licence and must follow your local regulations, band plans, and power limits. Never transmit without the proper licence, and treat every result here as a planning guide, not professional or legal advice.
Versión en español: Calculadora de Distancia entre Grid Squares – Distancia y Rumbo entre Dos Cuadrículas Maidenhead