Geodetic Distance Calculator

Ask two different tools how far apart two coordinates are and you will often get two different answers, several hundred metres apart. Neither is broken. One is treating the Earth as a sphere, the other as the squashed ellipsoid it actually is, and this Geodetic Distance Calculator shows both so you can see the gap rather than wonder about it.

Type two latitude and longitude pairs and you get the distance in six units, the bearing to set off on, the bearing you arrive at, and the midpoint of the route.

A Real Example: Dhaka to Chittagong

The tool opens on 23.8103, 90.4125 and 22.3569, 91.7832:

• 213.610 km by Vincenty on WGS-84, which is 132.731 miles or 115.340 nautical miles
• 213.952 km by great circle on a sphere, so the sphere overstates this route by 342.86 m, about 0.160%
• Bearing 138.62° SE leaving Dhaka, arriving on 139.16° — the half-degree of drift is the convergence of the meridians
• Midpoint at 23.085078, 91.101555

Further presses walk through London to Paris, New York to Los Angeles, Sydney to Santiago and a near-equatorial pair where the two models disagree most.

Formula: Why Two Numbers Instead of One

The great-circle figure comes from the haversine on a sphere of radius 6,371,008.8 m. The ellipsoidal figure comes from Vincenty’s inverse solution, which iterates on the WGS-84 flattening of 1/298.257223563 until successive passes agree to within 1e-12 radians, typically in four or five rounds. Vincenty is the one to quote: it is accurate to well under a millimetre on ordinary routes, where a sphere can be out by a fifth of a percent. Its one weakness is the near-antipodal case, where the iteration will not settle. Rather than return a wrong number, the tool stops after 200 passes, says so, and falls back to the great-circle answer.

What It Accepts in the Coordinate Boxes

Decimal degrees are the obvious form, but the parser also reads the degrees-minutes-seconds people copy off charts and GPS screens. -33.8688, 33 52 7 S and 33°52'07"S are all the same latitude, and a trailing S or W flips the sign for you, so you never have to convert by hand first. Every result is echoed back in DMS at the bottom, which is the quickest way to check you typed what you meant. Out-of-range values are caught rather than wrapped: a mistyped 233.8103 earns “First latitude must be between -90 and 90 degrees — 233.8103 is off the globe.” Distances follow the surface and ignore terrain, so a mountain route is longer on foot than the figure here.