Distance Calculator

As the crow flies, and why the crow is not helping

This is the great-circle distance: the shortest path along the surface of the earth between two points, which is the number an airline route map shows and the number a phone means when it says a restaurant is 400 m away. It is not the distance you will travel. Road distance between two places is typically 20 to 40 per cent longer than the straight line — traffic engineers call that ratio circuitry, and on a flat well-connected network it sits around 1.2 to 1.3. Mountains, rivers, coastlines and borders push it much higher: a pair of towns on opposite sides of a fjord or a range can be five kilometres apart and a hundred kilometres by road.

• Short distances are the worst case. Over a few kilometres in a city the ratio is dominated by one-way systems and rivers, and a straight line of 2 km can be a 6 km drive. Over a thousand kilometres the motorway network averages out and the ratio settles down.
• Flights are not straight lines either. They follow airways, avoid closed airspace and weather, and take the jet stream into account — which is why the same route is routinely an hour quicker eastbound than westbound across the Atlantic.
• The times here are arithmetic, not routing. Distance divided by an assumed speed, with the assumption printed next to it. They are for a sense of scale. Use a router for a plan.

What the numbers are calculated from

Haversine, on a sphere of mean radius 6,371 km. That is accurate to roughly half a per cent against the true ellipsoidal figure — up to about 20 km on a 4,000 km route, and the error is largest on long north-south paths. The cities in the list are single points at the centre of each place, so a "distance" between two points within one city is not a meaningful number, and the distance between two large cities is really the distance between two arbitrary points inside them. For anything with consequences — a freight quote, a flight plan, a boundary — use the actual coordinates of the actual endpoints, which this tool will take if you paste them.

Nautical miles, and why they exist

A nautical mile is one minute of latitude: 1,852 metres by definition. That is not a curiosity, it is the whole point — on a chart, a navigator can measure a distance against the latitude scale up the side of the paper with dividers and read it off directly. It is why marine and aviation speeds are in knots, one nautical mile per hour, and why this tool prints all three units rather than making you convert.