Distance is calculated as the great-circle ("as the crow flies") distance between city centres, using the Haversine formula. Actual flight or road distance will be longer.
There are three different numbers people mean when they ask how far one city is from another: the great-circle distance through the air, the actual flight path an airliner follows (which bends around restricted airspace and jet streams), and the road distance a car would drive. This tool calculates the first of these — the great-circle or "as the crow flies" distance — using the Haversine formula, the standard method for measuring distance between two points on a sphere using their latitude and longitude.
For most planning purposes this is the number you actually want: it's what airlines use as the baseline for scheduling and fuel planning, and it gives you a fair, comparable figure regardless of which airline or route is flown. A real flight path is typically 5–10% longer than the great-circle distance because of air traffic routing, and road distance can be anywhere from 15% to well over 50% longer depending on terrain and how directly roads connect the two points.
Great-circle distance is the fairest way to compare routes, because it strips out the specific quirks of any one airline's routing or any one road network's layout. If you're deciding between three possible destinations for a trip, comparing their great-circle distance from home gives you a like-for-like sense of how far each one really is, before booking-engine details like layovers or one operator's indirect routing distort the picture.
The tool also converts the result to an estimated non-stop flight duration using a typical airliner cruise speed, which is a quick way to sanity-check whether a "direct" flight time you've been quoted is plausible, or whether it's hiding an unusually long routing.
Every city in the list has a fixed latitude and longitude — its position on the globe. The Haversine formula treats the Earth as a sphere and works out the shortest path over that sphere's surface between the two points, accounting for the fact that the Earth is curved rather than flat, which matters a lot over long distances. Over short distances the curvature barely matters, but on routes like Mumbai to New York the difference between a flat-map estimate and the true great-circle distance is significant, sometimes hundreds of kilometres.
Once you have a distance figure, feed it straight into the Flight Fare Calculator to get a fare estimate for that route, or into the Mileage & Points Calculator to see roughly how many frequent-flyer miles the flight would earn. For a road trip instead of a flight, the Road Trip Route Planner chains several stops together and accounts for the fact that roads rarely run in a straight line.
It's also worth remembering that great-circle routes over long east-west distances, especially near the poles, can look counter-intuitive on a standard flat map projection — a route from New York to Tokyo, for instance, passes much further north than a straight line drawn on a typical world map would suggest, because the shortest path over a sphere often curves toward the nearer pole.
This tool measures the straight-line great-circle distance between two city centres. Real flights add distance for air traffic routing, weather diversions and the specific departure and arrival airport locations, so the true flown distance is usually a bit longer.
Not directly — road distance depends on the actual route roads take, which can be significantly longer than the straight-line distance, especially across mountains, coastlines or countries without direct highways. Use this figure as a lower bound, not a driving estimate.
A fixed reference point close to the city centre or its main airport reference point, which is standard practice for city-to-city distance figures.
Almost always, but wind patterns like jet streams can make an eastbound flight noticeably faster than the equivalent westbound flight over the same great-circle distance.