Ever wondered how a tool instantly knows two cities are 3,470 miles apart? It comes down to some elegant geometry applied to the curved surface of the Earth. Here's how it works, in plain terms.
Coordinates Come First
Every place can be pinpointed by its latitude and longitude. The first step in any distance calculation is converting place names into these coordinates — that's what location search and geocoding do behind the scenes.
The Haversine Formula
Because the Earth is roughly a sphere, you can't just use flat-map geometry over long distances. The haversine formula calculates the great-circle distance — the shortest path between two points along the surface of a sphere — using the two sets of coordinates and the Earth's radius. This gives the straight-line ("as the crow flies") distance.
From Straight-Line to Road Distance
Since roads aren't straight, tools estimate driving distance by applying a "circuity factor" to the straight-line distance — typically multiplying by around 1.2–1.4 to reflect how much longer real roads are. For precise routing, mapping services compute the actual road network path instead.
Why Estimates Vary
Different tools use slightly different Earth radii, rounding, and circuity factors, so you'll see small differences between them. They're all approximations — useful for planning, but real journeys depend on the exact roads, routes, and conditions.
Frequently Asked Questions
First, place names are converted to latitude and longitude coordinates. Then the haversine formula calculates the great-circle distance — the shortest path across the Earth's curved surface. For driving distance, a circuity factor is applied to estimate how much longer the actual roads are.