Distance Between Cities: Measuring the Straight Line on a Round Planet
When you ask how far one city is from another, there are really two different answers. One is the distance a bird would cover flying directly from point to point. The other is the distance your car actually drives, weaving around mountains, rivers, and borders. The Distance Between Cities tool gives you the first number — the great-circle, as-the-crow-flies distance — calculated instantly in your browser from the coordinates of each city.
That straight-line figure is the honest baseline. It tells you the true geographic separation between two places, independent of which roads exist or how heavy the traffic is. Once you know it, every other kind of distance becomes easy to reason about.
Straight-line distance versus driving distance
Straight-line distance ignores everything in between: no roads, no terrain, no detours. It is the shortest possible distance measured directly across the surface of the globe. Driving distance, by contrast, follows real roads that bend around lakes, climb over passes, and respect political boundaries.
The gap between the two is surprisingly predictable. In most regions, driving routes run about 1.2 to 1.5 times longer than the straight line, with a typical rule-of-thumb multiplier of roughly 1.3 in the United States. In cities split by water or hills — San Francisco, Pittsburgh — that ratio can climb past 2.0 for many trips. Flights, on the other hand, hug the great-circle path closely: long-haul routes usually add only 2 to 10 percent over the direct distance.
So if the tool tells you two cities are 500 km apart in a straight line, you can expect a drive of roughly 600 to 750 km and a flight only slightly longer than the 500 km baseline.
How great-circle distance is computed
Because the Earth is round, the shortest path between two surface points is not a straight line through the planet — it is an arc that curves along the surface. That arc is part of a great circle, the largest circle you can draw on a sphere. This is why long flight paths look curved when drawn on a flat map: they are actually straight in real life, just bent by the projection.
To measure that arc, the tool uses the haversine formula. In plain terms, it takes the latitude and longitude of each city, looks at the difference between them, and works out the angle between the two points as seen from the center of the Earth. Multiply that angle by the planet's radius — about 6,371 km on average — and you get the surface distance. The haversine approach stays numerically stable even for points very close together, which is why navigators have relied on it for generations.
The result is an approximation, but a good one. Because the Earth is a slightly flattened ellipsoid rather than a perfect sphere — wider at the equator than between the poles — the error stays under about half a percent. For travel planning, logistics estimates, and everyday curiosity, that precision is far more than enough.
Kilometres or miles
Distance is just a length, so converting between units is simple: one kilometre equals about 0.621 miles, and one mile equals roughly 1.609 kilometres. The tool shows both so you do not have to do the arithmetic. If a result reads 800 km, that is close to 497 miles; a 1,000-mile gap is about 1,609 km. The underlying great-circle calculation is identical either way — only the label on the number changes.
Practical uses
Knowing the direct distance between two cities helps in plenty of everyday situations. Travelers use it to sanity-check flight times and compare whether driving or flying makes sense for a given trip. Logistics and shipping teams lean on the straight-line figure as a quick baseline before layering on the road circuity factor to estimate real delivery distances and fuel. People plotting a move, a road trip, or a relocation use it to grasp how far apart two places truly are.
And sometimes it is pure curiosity — how far is your hometown from a city you have always wanted to visit? The straight-line number answers that in a way no winding road map can. If you want to dig deeper into the coordinates behind a place, pair this tool with our geolocation lookup, or browse the reference tables for related units and conversions.
Everything is computed locally in your browser from the city coordinates, so there is nothing to install and no waiting on a server. Enter two cities, read the arc, and you have an accurate measure of the world between them.
Frequently asked questions
What does as-the-crow-flies distance mean?
It is the straight-line, great-circle distance measured directly across the surface of the Earth, ignoring roads, terrain, and obstacles. It is the shortest possible distance between two points on the globe.
Why is the great-circle distance shorter than the driving distance?
Driving distance follows real roads that detour around water, mountains, and borders, so it is almost always longer. Driving routes typically run about 1.2 to 1.5 times the straight-line distance.
How accurate is the haversine calculation?
It is accurate to within roughly half a percent. The small error exists because the Earth is a slightly flattened ellipsoid rather than a perfect sphere, but for travel and planning purposes the result is more than precise enough.
Can I see the result in both kilometres and miles?
Yes. The tool shows both units side by side. One kilometre equals about 0.621 miles and one mile equals about 1.609 kilometres, so you never need to convert by hand.
Does the calculation send my data to a server?
No. The distance is computed entirely in your browser from the coordinates of the two cities. Nothing is uploaded, and the result appears instantly.
Why do long flight paths look curved on a map?
A great circle is actually straight on the globe, but flat-map projections bend it. The curve you see on a map is the projection distorting a path that is genuinely the shortest route in real life.