Great Circle Distance Calculator
Distance between two points on the globe from latitude and longitude — decimal or DMS — in km, miles and nautical miles, plus initial and final bearing. Nothing leaves your browser.
Also available as a desktop app for Windows.
About this tool
The shortest path between two points on a sphere is an arc of a great circle — a circle whose centre is the centre of the sphere. That is why a flight from New York to London curves noticeably north on a flat map: the straight line you would draw is not the shortest route, and over 5,500 km the two differ by hundreds of kilometres. This calculator works on the sphere, so the number it gives is the one an aircraft or a ship would measure.
Distances use the haversine formula on a sphere of radius 6,371.0088 km (the IUGG mean radius), which puts results within about 0.5% of the true ellipsoidal figure — close enough for any practical "how far apart are these?" question, and honest about being an approximation rather than claiming a precision it does not have. Unit conversions, by contrast, are exact: a mile is defined as 1.609344 km and a nautical mile as 1.852 km, so nothing is rounded on the way between units.
Bearings are given for both ends. The initial bearing is the compass heading you leave on; because a great circle keeps changing heading as it goes, the bearing at the far end differs — often by tens of degrees on a long north–south route. Input accepts both decimal degrees and degrees/minutes/seconds, which is the form most charts and aviation documents still use, and longitudes beyond ±180 wrap onto the globe rather than being rejected.
Frequently asked questions
- Why does the flight path look curved?
- It is not curved on the globe — it is curved on the flat map. The shortest route between two points is a great circle arc, and any projection that flattens the sphere will bend it. A New York–London flight does bend appreciably north, because the great circle runs further north than a line drawn straight across a Mercator chart would.
- How accurate is this compared with the real earth?
- The earth is an oblate spheroid, slightly flattened at the poles, while this calculator treats it as a sphere of mean radius 6,371.0088 km. The difference in the resulting distance is under about 0.5% — for London to New York, roughly 20 km on a 5,540 km figure. That is well inside the uncertainty of "which exact runway-to-runway points" you would compare against anyway.
- What is the difference between the initial and final bearing?
- A great circle is not a constant compass heading — it spirals relative to the meridians. The initial bearing is the heading when you set off; the final bearing is the heading you would be on arriving. On the JFK–London example the initial bearing is about 51° and the final about 108°, an indication of how much the heading rotates over a long route.
- What format should I type the coordinates in?
- Either decimal degrees with a hemisphere letter or sign (40.6413 N, or -73.7781), or degrees/minutes/seconds (40° 38′ 23″ N, or 40d 38m 23s N). A hemisphere letter and a minus sign together are rejected, since they would contradict each other. Minutes and seconds must be under 60 — 60.5 minutes is a typo, not a value.
- What is a nautical mile and why is it different?
- A nautical mile is defined as exactly 1.852 km, and it was traditionally one minute of latitude — which is why one degree along the equator comes out to almost exactly 60 nautical miles (60.04 here). Mariners and aviators use it because distances on a chart can be read straight off the latitude scale.
- Does it send my coordinates anywhere?
- No. Every calculation is plain arithmetic in the page. There is no server, no request and no logging, and the tool keeps working with the network switched off — a practical way to verify the claim yourself.