Distance between two cities
Type two cities in the world and pick from the suggestions: calculate the straight-line distance. Over 170,000 cities included.
What it's for
It calculates the «as the crow flies» (great-circle) distance between any two cities in the world: over 170,000 cities are included, from capitals to small towns. Start typing and pick the city from the suggestions.
Note
The distance is the direct line between the two points, not the road route (which is always longer). The city list is downloaded the first time you open this tool, then it stays fast.
What «as the crow flies» means
The distance calculated is the great-circle arc, the shortest path on the surface of a sphere: it is the route an unconstrained aircraft would fly and the number used for delayed-flight compensation. It is not the road distance, which is always longer.
The typical gap between road and straight line is 20-30% on flat ground and can exceed 60% in the mountains or where a sea sits in between. Rome to Milan is 477 km in a straight line and about 570 by motorway; Genoa to La Spezia is 80 straight and 100 by road.
Why the route looks curved on a map
On flat maps long routes look like arcs bending north, and that is not a mistake: on the Mercator projection the shortest line is not a straight one. Rome to Los Angeles passes over Greenland because up there the meridians converge and the way really is shorter.
It is the same reason flat maps distort areas: Greenland looks as big as Africa while it is fourteen times smaller. Distances on a sphere are computed with spherical trigonometry, not measured on the paper.
The Earth is not a perfect sphere
The standard sum uses a sphere of mean radius 6,371 km, but the planet is flattened at the poles by some twenty kilometres. On long routes the difference between the spherical model and the WGS84 ellipsoid reaches a few kilometres, less than 0.5%.
For normal use the sphere is more than enough, and it is also what European flight compensation rules ask for. The ellipsoid is needed only for precision navigation and land registry work, where a few metres genuinely count.
Nearby tools
If you need the number for a flight, Flight duration and Delayed flight compensation start from exactly this. To move between coordinate formats there is GPS coordinates DD→DMS.