How to draw range rings
This page opens with rings of 25, 50 and 100 nautical miles. Type a town or coordinates in the search box to centre them (for an airport or a harbour, paste its coordinates, for example 40.6413, -73.7781), or click the map. To change the rings, type new radii separated by commas in the radius box, for example 50, 100, 150, 200, and click the centre point again: every value becomes a ring around the same spot.
Each ring lists its area in square nautical miles and square kilometres, and its circumference. Drag a centre to move a ring, or type an exact radius in the list.
Reading the rings on the map
Distances over the Earth’s surface don’t stay the same size on a flat map. This map uses Web Mercator, like most online maps, which enlarges everything with latitude: a 100 nautical mile ring near Anchorage (61°N) is drawn about twice as large as the same ring near Singapore, and a 1,000 nautical mile ring is visibly taller than it is wide. That is correct: the outline is made of points each exactly the radius away from the centre, computed with Vincenty’s formulas on the WGS84 ellipsoid. Over the 180th meridian the rings continue on the other side of the map.
Distances and bearings
Switch to measure a distance and click two points for the great-circle distance in nautical miles (with kilometres alongside) and the initial true bearing. On long routes the bearing changes along the way, because a great circle crosses each meridian at a different angle.
Export the rings as KML for Google Earth or GeoJSON for GIS software, or Print them with a table of radii. These rings are a planning aid, not a navigation product.