Click the map to trace a shape, or paste GeoJSON below. You get the geodesic area and perimeter in every unit that matters — with holes subtracted properly.
Most quick area calculations project coordinates onto a flat plane and apply the shoelace formula. That is fast, easy, and increasingly wrong the further you get from the equator, because lines of longitude converge as they approach the poles. A one-degree box in Kenya covers far more ground than a one-degree box in Iceland.
This calculator uses spherical excess instead, treating the Earth as a sphere of mean radius 6,371,008.8 m. The remaining error against a true ellipsoid is under about 0.5% anywhere on the planet — well below the precision of the coordinates you are likely feeding it.
| Unit | Equivalent | Typical use |
|---|---|---|
| Square metre (m²) | — | Buildings, yards, small zones |
| Hectare (ha) | 10,000 m² | Farmland, parks (metric standard) |
| Acre | 4,046.86 m² | Land in the US, UK, and Ireland |
| Square kilometre (km²) | 1,000,000 m² | Districts, delivery regions |
| Square mile (mi²) | 2,589,988 m² | US counties, large service areas |
Useful reference points: a football pitch is roughly 0.7 ha (1.76 acres), and a city block in Manhattan is about 1.6 ha.
A GeoJSON Polygon holds an array of rings. The first ring is
the outer boundary; each subsequent ring is a hole. This calculator
computes the outer ring's area and subtracts every hole — so a delivery
zone with an excluded block in the middle reports the area you can
actually serve, not the area of the outline.
Ring winding direction is ignored. RFC 7946 asks for counter-clockwise outer rings and clockwise holes, but real-world exports are inconsistent about it, and area should not depend on which way a file happened to be written. If you want to check whether your winding is correct for stricter tools, the GeoJSON viewer renders the structure so you can see what a parser sees.
More vertices does not mean more accuracy. Once your spacing between points drops below the accuracy of the coordinates themselves, you are just tracing measurement noise into the boundary. For a zone built from consumer GPS readings, points closer together than about 10 metres add nothing.
This matters practically because vertex count affects every subsequent point-in-polygon test. A 500-vertex shape costs meaningfully more to check than a 20-vertex one, multiplied by every position report from every device, forever. Trace the shape you need and stop.
Knowing a zone's area is often the first step toward using it as a geofence. Once the shape is right, the geofence builder exports it as GeoJSON, the distance calculator helps you sanity-check the dimensions, and Geoblip can watch it — alerting you by email or push the moment a tracked device crosses the boundary you just drew.
This tool draws the boundary. Geoblip watches it — assign a phone or GPS tracker, set the hours it should be active, and get an email or push notification the moment it crosses the line.