Great Circle Distance Calculator

Because a great circle route is not a single constant compass heading -- except when flying due north/south or along the equator, the true course changes continuously as you travel along the shortest path over a sphere. Initial True Course is only the heading at departure; Final Bearing is the heading you'd be flying on arrival, and for two genuinely different points the two are generally different by design, not by error. (If you enter identical departure and destination coordinates as a sanity check, both bearings correctly read 0° -- there's no course to fly between a point and itself.)

Close, but not identical. This calculator uses the Haversine formula on a spherical-Earth model (a fixed mean radius), while GPS receivers and certified flight-management systems use the WGS84 ellipsoid, which accounts for Earth's actual oblate shape. The difference is typically well under half a percent for most routes -- fine for flight planning and estimation, but not a substitute for certified navigation data.

It marks the geographic halfway point along the actual great circle path between your two coordinates -- not a simple average of the latitude and longitude values, which would not generally sit on the route at all. Midpoint Longitude is normalized to the standard ±180° range, so a route that crosses the antimeridian (the trans-Pacific case pilots most often use this for) still reports a valid coordinate instead of a value outside ±180°. Pilots and dispatchers use a route's midpoint to help identify enroute alternates or evaluate ETP (equal-time point) planning for long overwater or remote-area legs.

No. Est. Time at 120 kt and Est. Time at 450 kt are simple great-circle-distance- divided-by-speed calculations -- they ignore headwind or tailwind components, climb and descent segments, and any real-world routing that deviates from the direct great circle path (which airspace structure and air traffic control routing almost always require). Treat them as rough planning estimates, not a replacement for a real flight-planning computation.