RavingDesk Geodesic Distance & Bearing Calculator

What it is for

Most "distance between coordinates" calculators treat the Earth as a perfect sphere. The Earth is slightly flattened, so a spherical formula such as Haversine can be off by up to about half a percent, and by different amounts in different directions. That is fine for a rough estimate. It is not fine when you check a survey, plan a flight leg, compare GPS logs or need a number that agrees with professional GIS software.

This calculator measures on the WGS84 ellipsoid (the one GPS uses) with Karney's geodesic algorithm. It works for any pair of points, including nearly opposite points where the older Vincenty method fails to converge. Enter two points for a single distance, or a list of points for a route, optionally closed back to the start. You can type coordinates in decimal degrees, degrees-minutes-seconds, UTM, MGRS, plus codes or Maidenhead locators, and mix them.

It does not follow roads or terrain. The distance is along the ellipsoid surface, and heights are ignored.

Worked example

From New York JFK to London Heathrow, entered as 40°38′23″N 73°46′44″W and 51.4700, -0.4543:

The sphere comes out almost 15 km short on this transatlantic leg. The bearings show how a long geodesic curves on a map: you leave JFK heading north-east (about 51°) and arrive in London heading east-south-east (about 108°). The midpoint lies far north, over the Atlantic south of Greenland. The "Points as read" table confirms that the DMS text was read as 40.6397222, −73.7788889.

For a route, the built-in example walks past seven Berlin landmarks: 4.156 km in six legs, against 4.148 km on the sphere. The direct distance from the Reichstag to the TV Tower is 2.276 km.

How to read the result

• Geodesic distance / Route length is the shortest path on the ellipsoid, summed over all legs. This is the number to use.
• Haversine (sphere) is the same route on a sphere with the mean Earth radius. The difference shows how much the simple formula would be off.
• Initial and final bearing are measured clockwise from true (geographic) north. On long legs they differ, because the shortest path is not a line of constant compass heading.
• The Legs table lists each leg with its cumulative distance. Points as read shows how each coordinate was understood and in which notation.

Tips and common mistakes

• Separate latitude and longitude with a comma. Hemisphere letters (N, S, E, W) may come before or after the numbers.
• Latitude comes first unless you use hemisphere letters. 13.405, 52.52 is read as a point in the Indian Ocean, not Berlin.
• MGRS, plus codes and locators stand for squares. The centre of the square is used, and a warning appears for squares larger than 100 m.
• Add the local magnetic declination before you use a bearing with a compass.
• The ellipsoid setting matters only for old maps. GPS and web maps use WGS84, which matches GRS80 to well under a millimetre.

FAQ

How accurate is it?

Karney's algorithm is accurate to about 15 nanometres on WGS84. The tool reproduces Vincenty's published 1975 test lines and the GeographicLib test set, including nearly antipodal lines.

Why not just use Haversine?

Haversine is simple and usually within 0.5 %, but the error depends on direction and latitude. Over 5,000 km that can be 15 km, as in the example above.

Can I measure a closed area's perimeter?

Yes. List the corners and tick "Return to the first point". For the area itself, use the RavingDesk GeoJSON inspector.

Where can I see the route on a map?

In RavingDesk's Data & charts, add a Geo layer step to a table of points. It shows the same distances on an offline map.