What is a great-circle route?

A great circle is the shortest path between two points on the surface of a sphere, which is why long flights appear to curve toward the poles on a flat map. The tool computes this shortest distance and the course you start out on along it.

Why does the course change along the route?

Unlike a constant-heading rhumb line, a great circle continuously changes its true course as you travel. The tool reports the initial true course at the origin, and the waypoints let you re-check the course as you progress along the route.

How is the distance computed?

It uses the haversine formula on a spherical Earth with a radius of 3440 nautical miles. This is accurate to a fraction of a percent for route planning, though precise navigation databases use a slightly flattened ellipsoid model.

How are the waypoints calculated?

The tool uses spherical interpolation along the great circle, placing each waypoint at an equal fraction of the total angular distance. This gives true points on the shortest path rather than a straight line drawn on a flat chart.

Are these true or magnetic courses?

The initial course is true, referenced to true north. To fly it you must apply local magnetic variation, which changes along the route, so oceanic plans often track true course and apply variation at each waypoint.

Great-Circle Aviation Route Calculator

The shortest route between two airports follows a great circle, the curved path that looks longer on a flat map but is actually the most direct. This calculator returns the great-circle distance, the initial true course, and a set of en-route waypoints for any two coordinates.

How it works

Distance comes from the haversine formula and the course from the standard initial-bearing formula:

a = sin²(Δφ/2) + cos φ1 · cos φ2 · sin²(Δλ/2)
distance = 2R · atan2(√a, √(1−a))        R = 3440.065 nm
course   = atan2( sinΔλ·cosφ2 ,
                  cosφ1·sinφ2 − sinφ1·cosφ2·cosΔλ )

Waypoints are placed by spherical interpolation, so each one sits on the true great circle at an equal fraction of the total distance.

Example and notes

From London Heathrow (51.4775, −0.4614) to New York JFK (40.6413, −73.7781) the great-circle distance is about 3,000 nautical miles with an initial true course near 288 degrees, even though both airports are at similar latitudes. The course swings noticeably as you cross the Atlantic, which is why the generated waypoints matter: re-check the course at each one, and apply the local magnetic variation to fly the magnetic heading.