Enter two GPS coordinates to get the great-circle distance and the initial bearing from the first point to the second. Accepts decimal degrees or DMS notation.
This is the great-circle distance — the shortest path between two points across the surface of the Earth, computed with the haversine formula. It is not driving distance, and it is not a straight line through the planet. Think "how far a bird flies", not "what your satnav says".
Driving distance is typically 20–40% longer than great-circle distance, because roads bend around terrain and property. If you need road distance, you need a routing engine, not a geometry formula.
The bearing is the initial compass heading from point A to point B, measured clockwise from true north. On a sphere it changes as you travel — following a great circle from Lisbon to New York, you set off heading roughly west-northwest and arrive heading southwest. That is why "initial" matters, and why the reverse bearing from B to A is usually not simply 180 degrees away.
The haversine formula treats the Earth as a perfect sphere. The Earth is slightly flattened at the poles, so results carry up to about 0.5% error — around 5 metres per kilometre. For anything involving consumer GPS this is irrelevant: a phone's own position is uncertain by 5–10 metres in the open and considerably more in a city, which swamps the formula's error many times over.
Geodesic methods on an ellipsoid (Vincenty, Karney) reduce the error to millimetres. Use them for surveying and aviation. For working out whether a delivery van is near a customer, haversine is more than enough.
The most common use of this calculation in tracking is picking a geofence radius. Two rules from practice:
To draw and export that circle directly, use the radius map tool. For irregular shapes — a school campus, a depot, a park — the geofence builder lets you trace the real outline instead, and the area calculator tells you how much ground it actually covers.
Points either side of the 180° meridian (near Fiji, or the Bering Strait) break naive distance code that subtracts longitudes directly. The haversine formula handles this correctly because it works in trigonometric terms rather than raw differences — so a calculation from 179°E to 179°W correctly returns about 220 km, not 40,000 km.
This tool draws the boundary. Geoblip watches it — assign a phone or GPS tracker, set the hours it should be active, and get an email or push notification the moment it crosses the line.