Great Circle Distance Tool
Enter two points in decimal degrees. The calculator returns the shortest path over the Earth's surface, plus bearing and midpoint.
What Is a Great Circle?
A great circle is the largest possible circle you can draw on a sphere. On Earth, the equator and all meridians are examples. If you want the shortest route between two locations on a globe, you travel along a segment of a great circle.
This matters because maps are flat, but Earth is not. A route that looks curved on a map can be the true shortest path in real life. That is why long-haul flights often arc over oceans or polar regions instead of following what appears to be a straight line on a paper map.
How This Great Circle Calculator Works
The calculator uses the haversine formula, a standard method for finding distance between two points defined by latitude and longitude on a sphere. It takes the two coordinates, converts degrees to radians, computes the central angle, and multiplies by Earth’s radius in your selected unit.
Outputs Included
- Great-circle distance: shortest surface distance between Point A and Point B.
- Central angle: angular separation between the two points.
- Initial bearing: the compass heading to start from Point A toward Point B.
- Midpoint: approximate geographic midpoint along the great-circle route.
Why This Is Better Than Flat-Map Distance
A simple flat distance (like Euclidean x/y distance) ignores Earth’s curvature and can be very inaccurate over long ranges. Great-circle distance is the standard for aviation, marine navigation, geospatial analytics, satellite planning, and route estimation.
How to Use the Calculator
- Enter latitude and longitude for Point A.
- Enter latitude and longitude for Point B.
- Select km, miles, or nautical miles.
- Click Calculate Great Circle.
Coordinate format should be decimal degrees. North and East are positive; South and West are negative.
Example: New York is approximately 40.7128, -74.0060.
Common Use Cases
- Estimating flight or shipping route lengths.
- Planning long-distance travel paths.
- Studying geographic datasets in GIS projects.
- Comparing route efficiency between city pairs.
- Building educational demos for earth science or navigation.
Accuracy Notes
This calculator assumes a spherical Earth with a fixed radius. For most practical needs, that is excellent. Professional surveying and high-precision geodesy may use ellipsoidal models (like WGS84) for slightly more accurate results at very fine scales.
Tips to Avoid Input Errors
- Latitude must be between -90 and 90.
- Longitude must be between -180 and 180.
- Do not swap latitude and longitude fields.
- Use decimal points, not degree-minute-second format.
Quick Example
Try Point A: 40.7128, -74.0060 (New York) and Point B: 51.5074, -0.1278 (London). You should get a distance around 5,570 km (depending on radius choice and rounding).
Final Thoughts
Great-circle calculations are one of those deceptively simple tools that unlock a lot of practical insight. Whether you're planning travel, building geospatial software, or learning navigation fundamentals, this calculator gives you a reliable and fast starting point.